The idea is that if you own 5% of a company worth 200M and you quit, the remaining 95% ownership of the company cares enough about it that they will replace you

The idea is that if you own 5% of a company worth 200M and you quit, the remaining 95% ownership of the company cares enough about it that they will replace you and move on. In this scenario there is no acquisition, and you walk away without making the company lose any significant value. I've seen that happen: one of the fully vested founders of the company I worked for left on a sabbatical. After six months he decided he didn't want to come back. By then all his functions had been taken over by other people. He sold some of his stock, kept the rest and went back to grad school. The point is not so much the size as the fact that you can walk away more easily if you own a small fraction of a company without causing a significant drop in value.