Even if your mutual fund manager is a bona fide genius, it's unlikely he has more than 5 or 6 good investment ideas a year. You want your mutual fund manager's best ideas, not the 200 mediocre ones. Once a mutual fund gets too large, the manager has to buy large capitalization stocks for liquidity . Also there are restrictions on how much of any one stock they can hold. Celebrities, restaurant owners, taxi drivers, lawyers, teachers, students, and your average everyday person have all become stock pickers.
People have many different ways to pick stocks.
Some people will only look at companies which have good earnings and sound fundamentals. Others will look at the core of the business and determine if the products or services offered is better than it's competitors. Others again might only look at the charts of stocks and try to determine if the stock is going higher or lower.