Warren Buffett says

“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.”

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“We both insist on a lot of time being available almost every day to just sit and think. That is very uncommon in American business. We read and think. So Warren and I do more reading and thinking and less doing than most people in business.”