There are two schools of thoughts lets contemplate over them
Balanced diversification
Rohit Chauhan – On his blog [Emphasis Mine]
My bet or size of the position is generally 2% or 5 % and a max of 10% if my level of confidence is very high. However I am not into portfolio balancing. So if my best idea has done well and is now say 20% of my portfolio and I think is still undervalued, I let it run and remain in the portfolio. The only time I would sell would be if the fundamentals of the company deteriorate or the company becomes highly overvalued
Concentration
Warren Buffet – 1965 letter to Partners [Emphasis Mine]
I am willing to give up quite a bit in terms of levelling of year-to-year results (remember when I talk of “results,” I am talking of performance relative to the Dow) in order to achieve better overall long-term performance. Simply stated, this means I am willing to concentrate quite heavily in what I believe to be the best investment opportunities recognizing very well that this may cause an occasional very sour year – one somewhat more sour, probably, than if I had diversified more… Read the rest