What an investor needs is the ability to correctly evaluate selected businesses. Note that word โselectedโ: You don't have to be an expert on every company, or even many. You only have to be able to evaluate companies within your circle of competence. The size of that circle is not very important; knowing its boundaries, however, is vital.
Warren BuffettYou will be right, over the course of many transactions, if your hypotheses are correct, your facts are correct, and your reasoning is correct. True conservatism is only possible through knowledge and reason.
Warren BuffettIf you are a professional and have confidence, then I would advocate lots of concentration.
Warren Buffett