By sheer coincidence, while reading the book How doctors think, I got into a conversation with a neighbour who believes that all that most Indian doctors do with their patients is "...R and D (research and development). Doctors can never seem to make a firm diagnosis. What's so difficult about it?" He also believes that it is possible for technology to be developed to such an extent that correct diagnosis can be made and appropriate, personalised medicine be practised in the future. My attempts to explain that medicine and, more importantly, disease does not follow a linear, structured pattern have fallen on deaf ears. This, then, is a book for people like my neighbour. It attempts to explain to the layperson the different factors that go into the making of a medical decision, whether in making a diagnosis or for offering therapeutic options.