I read this on Alpha Ideas blog yesterday.
Let's assume an individual's core competence is pharma, & he has been investing long enough. He would have made a lot of money by investing in Ajanta, Lupin, etc. Even before the USFDA problems, he might have noticed earlier than others the trend of price erosion in US. And now, it's a case of either holding on, or adding more, or switching over to other stocks. Here again, he probably has better insight than others, especially while making the decision to sell off a winner.
For the sake of balance, let's assume he isn't good at assessing the financials of a company. He might have invested in Opto Circuits, and burnt his finger.
If we assume this individual started off only a few years ago. He would likely have Shilpa, Natco, Biocon, etc (Basically, identify the potential for companies manufacturing Oncology drugs) & his portfolio would do just fine.
In terms of diversification, he could look into Hospitals, Diagnostics, Health Insurance, Medical device companies.
At the end of the day, it's simply a case of sticking to one's circle of competence. When this competence is exceptional, the probability of landing that huge winner goes up. In my opinion, Bruce Lee would do just fine.
P.S. I acknowledge that this reply has a degree of hindsight bias.