If diseases could answer questions, doctors would have far fewer sleepless nights.

We could simply sit them down and ask. Why the kidneys? Why not the liver? Why did you simply scar the retina but spare the heart? Why did you choose the joints yet leave the muscles alone? Why did you settle in the skin of one patient but in the lungs of another? Unfortunately, diseases are remarkably secretive. They never explain themselves. They simply arrive, choose one destination with unnerving precision, and leave physicians trying to reconstruct their motives long after the consultation has ended.

The mystery becomes impossible to ignore once someone points it out. Every minute, the human heart pumps blood through nearly one lakh kilometres of blood vessels. Glucose reaches virtually every living cell. Cholesterol circulates through the entire arterial tree. Hormones travel everywhere without prejudice. Yet disease behaves as though it carries a private map. Diabetes may quietly steal one person’s eyesight while another person’s kidneys slowly fail. A third loses sensation in the feet. A fourth develops heart disease. The bloodstream is shared. The destination is not.

Nor is diabetes unusual. Breast cancer frequently spreads to bone but surprisingly rarely to skeletal muscle, despite muscle making up nearly half the body’s weight and receiving abundant blood flow. Doctors know that psoriasis repeatedly returns to the elbows, knees, and scalp rather than appearing randomly across the skin. Neurologists have long been fascinated by shingles, which can remain dormant inside sensory nerve cells for decades before erupting along a single dermatome, respecting invisible anatomical boundaries with astonishing discipline. Orthopaedic surgeons have another puzzle. Osteoarthritis often attacks the hips and knees, yet the ankle—despite bearing the body’s weight every day—remains remarkably resistant unless it has suffered a prior injury. Diseases are not careless travellers. They appear to possess extraordinary powers of selection.

The first person who forced me to think seriously about this mystery was not a professor. It was a patient. He looked at his blood reports, sighed dramatically and announced, “Doctor, I think my kidneys are jealous.”

“Jealous of whom?” I asked.

“My neighbour’s kidneys.”

Both men had diabetes. His neighbour had lived with it for nearly twenty years and still had healthy kidneys. He himself had developed diabetes much later, yet early kidney damage had already appeared.

“So tell me honestly,” he said with a smile, “are kidneys capable of professional rivalry?” We laughed.

Then came the question hiding beneath the joke. “Why did diabetes choose mine?”

That sentence made me think. During college, we are taught why diabetes develops. We learn about insulin resistance, pancreatic beta cells, glucose metabolism and vascular injury. We become familiar with receptors, signalling pathways and biochemical cascades. They are all essential. Yet none of them completely answers my patient’s question. They explain how diabetes begins. They do not fully explain why the same disease writes such different stories in different people. Somewhere between rising blood sugar and failing kidneys lies another mystery.

That mystery has occupied some of medicine’s finest minds for well over a century. In 1889, the English surgeon Stephen Paget examined hundreds of women whose breast cancer had spread beyond the breast. At the time, many believed cancer cells simply lodged wherever blood flow carried them. Paget noticed something that refused to fit that explanation. Certain organs repeatedly became home to metastatic cancer, while others remained surprisingly untouched. He proposed what later became known as the Seed and Soil Hypothesis. A seed may travel everywhere, he argued, but it grows only where the soil is willing to receive it. More than a century later, cancer biology continues to refine that idea rather than replace it.

Modern science has since revealed just how different our organs really are. The retina is one of the few places where doctors can directly observe living blood vessels without making a single incision, and those delicate vessels are often among the earliest victims of diabetes. Each kidney contains about a million microscopic glomeruli that filter nearly 180 litres of fluid every day, performing an extraordinary task so silently that most of us never think about them until they begin to fail. The liver can regenerate after losing much of its tissue. The brain protects itself behind the highly selective blood-brain barrier, which excludes countless substances circulating elsewhere in the body. From the outside, we appear to possess one body. Under the microscope, we resemble an entire continent made up of different landscapes, each governed by its own biological laws.

The deeper biology looks, the more selective the disease appears. Scientists now know that cancer cells entering the bloodstream do not automatically become metastases. Most never succeed. Many die within hours. Some remain dormant for years. Only a tiny minority establish themselves because they encounter a tissue that provides precisely the right combination of nutrients, chemical signals and immune tolerance. Reaching an organ is relatively easy. Belonging there is extraordinarily difficult.

Years after leaving medical college, while reading about these discoveries, I experienced one of those delightful moments every physician secretly enjoys—the feeling that something entirely new was quietly echoing something very old. I had encountered this mystery before. Not in an oncology journal. Not in an immunology textbook. But in an Ayurvedic classroom, a teacher had spent barely a few minutes discussing a concept that seemed abstract enough to memorise for an examination and promptly forget afterwards.

Years later, sitting across thousands of patients, I realised that perhaps it was not the concept I had forgotten. It was the question. Ayurveda has been asking it for nearly two thousand years.

It is called the answer Khavaigunya.

The Sanskrit word is deceptively simple. Kha means a space, a passage or a channel within the body. Vaigunya means a defect, weakness or loss of normal integrity. Together, they describe a place that has become more vulnerable than the surrounding tissues. Not diseased. Not permanently damaged. Simply less capable of resisting what neighbouring tissues continue to withstand. It is less a diagnosis than a predisposition, less a disease than an opportunity waiting to be discovered.

That distinction is easy to miss but impossible to overstate. Imagine the first heavy rain after summer. The rain falls evenly across every rooftop in a neighbourhood. Yet only one house begins to leak. The rain is not different. The clouds are not selective. What differs is the roof. Somewhere beneath the tiles, a tiny crack has been widening silently for months. The storm merely reveals what was already there. Ayurveda suggests that disease often behaves similarly. The disturbance may travel widely, but it becomes an illness only where resilience has quietly diminished.

Classical Ayurveda places this moment during Sthanasamshraya, the fourth stage of Shatkriyakala, the six-stage evolution of disease. Until this stage, aggravated doshas are described as circulating through the body without producing recognisable illness. They disturb physiology but have not yet declared where the disease will finally appear. During Sthanasamshraya, they encounter a susceptible tissue—a Khavaigunya—and interact with the local dushyas, the body tissues. Classical texts describe this meeting as Dosha–Dushya Sammurchana. Disease is born not from the dosha alone or from the tissue alone, but from their interaction. It is one of the most elegant ideas in Ayurvedic pathology because it explains why the same disturbed dosha need not produce the same illness in every individual.

That single insight answers another question that puzzled me as a young physician. Why does one patient with aggravated Vata develop osteoarthritis while another struggles with insomnia, a third with chronic constipation and a fourth with neurological symptoms? If the dosha alone determined disease, everyone should become ill in the same way. Ayurveda proposes otherwise. The dosha may be similar. The destination is not. Disease reflects not only what has gone wrong but also where that disturbance finally finds a home.

For years, I regarded this as an elegant philosophical idea. Then my patients slowly persuaded me that it was also a practical clinical observation.

One of them was a civil engineer who had fractured his right ankle in a motorcycle accident when he was twenty-eight. Plates were inserted, the fracture healed beautifully, and life moved on. Nearly thirty years later, he developed inflammatory arthritis. What caught my attention was not the diagnosis but its curious behaviour. Almost every flare announced itself in that same ankle before spreading elsewhere. One afternoon, he laughed and said, “Doctor, my body remembers that accident better than I do.”

His sentence lingered with me because modern biology has been uncovering a remarkably similar truth. A tissue that has healed is not necessarily identical to the one that existed before injury. Blood vessels remodel. Collagen fibres reorganise. Nerve endings alter their sensitivity. Local immune cells can retain molecular memories of earlier inflammation for years. Researchers now speak of tissue remodelling, immune memory and persistent changes within the local microenvironment. Whether or not one uses the language of Ayurveda, the body clearly remembers more than we once imagined.

I encounter another fascinating example almost every week. A person living with psoriasis may develop fresh plaques precisely where the skin has been scratched, burned or repeatedly rubbed. Similar patterns are seen in vitiligo and certain other skin disorders. This is known as the Koebner phenomenon. The injury does not create the disease. Instead, it creates a local environment in which an existing disease finds expression. Once again, illness appears to require more than a trigger. It also requires a receptive place.

Notice what is happening here. Neither Ayurveda nor modern medicine is trying to reduce disease to a single cause. Both are moving away from simple explanations. Modern biology increasingly describes disease as an interaction between genes, immunity, metabolism and the local tissue environment. Ayurveda described it as the meeting of disturbed doshas with susceptible tissues. The scientific languages are different, the methods are different, and they should remain different. Yet both traditions arrive at the same humbling realisation: the body is not a uniform landscape. It is a collection of biological neighbourhoods, each with its own strengths, its own history, and sometimes its own hidden vulnerabilities.

That realisation quietly transformed the way I practised medicine. Earlier in my career, I was satisfied once I had identified the disease. Today, I find myself asking another question before writing the prescription. Why this tissue? Why now? What story has this organ been carrying long before today’s symptoms appeared? A diagnosis tells me what has happened. It rarely tells me why this particular place surrendered first. The longer I have practised medicine, the less interested I have become in dramatic causes.

Patients often arrive convinced that one stressful month, one wedding feast, one forgotten tablet or one sleepless night explains everything. The internet encourages this habit. Every few years, it discovers a new universal villain. Sugar. Gluten. Seed oils. Pollution. Stress. Social media then does what it does best—it converts a complicated biological conversation into a one-line verdict. The human body politely refuses to cooperate.

Most diseases resemble the slow weakening of an old bridge rather than the collapse caused by a single overloaded truck. Tiny changes accumulate quietly. Blood pressure remains slightly high. Blood sugar drifts upwards. Sleep grows shorter. An old injury never easily regains its original strength. Low-grade inflammation lingers unnoticed. Each change appears too small to matter. Together, they gradually alter the landscape on which disease eventually arrives. By the time symptoms become obvious, biology has often been whispering for years.

That is why two people rarely carry the same illness in exactly the same way. One patient with diabetes develops kidney disease, while another loses vision. One smoker reaches ninety with surprisingly healthy lungs, while another develops chronic lung disease decades earlier. One person recovers rapidly from a viral infection while another struggles with persistent fatigue for months. Medicine is slowly moving away from asking, “What disease does this patient have?” towards a far more interesting question: “How is this patient’s biology responding to the disease?” That change may prove to be one of the defining shifts in medicine during this century.

Curiously, this is also where Ayurveda feels unexpectedly contemporary. Its greatest strength was never that it identified every disease correctly or predicted every scientific discovery. No medical system can honestly claim that. Its enduring strength lay elsewhere. It insisted that the physician understand the individual before becoming fascinated by the illness. Constitution. Strength. Age. Diet. Occupation. Previous disease. Mental state. Seasonal influences. Long before the word personalised medicine entered scientific journals, Ayurveda had already placed individuality at the centre of clinical thinking. Perhaps that explains why experienced physicians gradually become better listeners than talkers.

Early in my career, consultations revolved around symptoms. Now they often revolve around stories. “When did this really begin?” “What was happening in your life before the pain appeared?” “Has this joint troubled you before?” “Was there an old injury?” Those questions rarely appear in blood reports. Yet they often explain the patient better than the blood reports do.

Patients occasionally ask me a question that deserves an honest answer. “Doctor, could this have been prevented?” Sometimes the answer is yes. Sometimes it is no.

Some diseases are shaped powerfully by inherited biology. Others appear despite disciplined lifestyles. Human beings are not machines assembled from identical components. We are living histories. Everybody carries their own inheritance, memories, injuries, adaptations and astonishing capacity for repair. Vulnerability is never the whole story. Resilience is quietly writing its own story at the same time.

I often think back to the gentleman who believed his kidneys were jealous of his neighbour’s. Months later, he returned with fresh reports. His blood sugar had improved. His kidney function had remained stable. As I finished writing the prescription, he smiled. “Doctor,” he said, “my kidneys and I have signed a peace treaty.” We both laughed.

Every generation of physicians inherits a handful of questions that refuse to grow old. This is one of them. We have learnt to replace failing hearts, sequence entire genomes and edit genes with astonishing precision. Yet a patient can still look across a consultation table and ask, “Doctor, why my kidneys?” It is a deceptively simple question that exposes the limits of everything we know. The day medicine answers it completely will not merely change the treatment of disease. It will change the way we understand the human body itself.