So I tend to focus on ideas that have a 1000x higher chance of success than the next un-monetizable social website you have in mind, but the success I strive for is a bit more modest. Probably close to 1/1000th of the payout of a big exit.
But I believe this approach is far more likely to make you happy, and far more likely to actually make a difference in the lives of more than the handful of people who hit the startup lottery each year.
That can't make his investors happy. Oh wait, he doesn't have any.