Clinical practice is being evolved during decades to improve the standards of patient care, diagnosis, and treatment. Evolution of medical practice from empirical treatment to evidence based medicine happened with the development of newer techniques and tools foraccurate diagnosis and practice. However, treatment options for many ailments were developed based on trials conducted in non-homogeneous numbers distinctly many times less than the population receiving medication after approval. During past years,we also witnessed awareness about pharmacovigilance and many medications were withdrawn after being associated with rare fatal conditions, which might occur in few tens and hundreds of patients among thousand and millions receiving the medication. This procedure of drug development (clinical) has always been a trial and error method to evaluate the benefits and risks; and due to the involvement of lots of investments, there is always peer pressure for the marketing of medication. Reasons for most of these rare events, and basis for the occurrence of these events in only a few patients, but not in all, have always been a problem to be investigated and were attributed to idiosyncrasy. The concept of medication i.e. â€œOne fits for allâ€ is in transformation towards theconcept of â€œOne fits One or Fewâ€ only.