Shareholder Activist

Carl Icahn is the most famous one. He buys big stakes (10%? 15%?) of companies that have performed poorly for a long time. He identifies 3-4 things that the company can do to immediately to goose its stock price (like...how about selling that fleet of jets you keep for your execs...or how about selling off the money-losing Somalia division...or how about just getting a new CEO who isn't, in fact, a drunk?) The activist buys shares. And remember: it's the common shares that elect the board, and since usually less than half of a company's total number of shares ever vote in elections, owning 15% is often enough to make huge changes in a company's management, especially when the stock has performed poorly for a long time.

So the big shareholder gets active. He rattles the cage of the company and hopes to generate value for his own shareholders. The system works for companies that have had bad results for a long time; not so much for companies that have done extremely well.

Like...try complaining that Jeff Bezos has done a bad job running Amazon and listen to the laughter you'll get from the major institutions that have owned the stock for the last decade or two.