Graduate in Physics. Post graduate in Biology. Won Nobel Prize for Chemistry in 2009. Do you know the name of this individual? Yes, it is Venkataraman Ramakrishnan.
When he was asked, in an interview, about these changes in his career,he said this is not at all surprising. He said " Science has no watertight compartments". He further added that if one looks at the list of Nobel Laureates in Chemistry, one will find that many are graduates in Physics. In other words, this is a norm, not an exceptional phenomenon.
Of course, scientists provide us an example of an individual, who changes discipline, because he sees some 'answer' which he is not finding in his existing discipline. He is driven by gain, so to say.
Most of individuals in normal life are driven to move from one discipline to another due to Pain. I met a IIT student last week. He is third year of IIT in Mumbai. He went to Kota for two years, studied hard, and got an admission in IIT. But he feels he is stifled by what he is seeing in Engineering. He was asking me if he could move to 'Management'.
During my coaching, I meet many students, who move to Engineering out of their own desire, but soon realise that they are not finding Engineering 'exciting'. Their growth has stopped for some reason. More often than not, they are unable to dive deeper in 1000 feet zone in their Engineering subjects. They feel like a fish out of water. On the other hand, they see some other students who are enjoying 'Engineering' and are doing exceedingly well with seemingly little effort. They realise that 'Engineering' is not for them. ( More often than not, they are right.)
Articles and commentators often jeer at these students and make them feel guilty. Some big leader also claims that 'if someone wanted to do management after IIT, why do students take up IIT'. However, for individuals who are making careers with their thinking competency this is absolutely normal.
They cannot find what they can do better before hand. ( No one really can!)And when they encounter an obstacle, they find another path. Infact, that is one of the great benefits of making career with thinking competency. Unlike doing competency individuals ( in sports, music and entertainment), thinking competency individuals change their professions and careers to find their calling. Only difference is that some individuals reach it through pain, while others reach it through gain.