1) If you want to hang out with "cool startup people" and be involved in "cool startup culture" just about any startup will do. No need to do something difficult. That recipe aggregator will do just fine.
2) If you want to work on "interesting" problems, there are lots of those too. They might not serve many people (dev tools which do the same thing as many other existing dev tools and do not improve upon them) or change the world in really useful ways, they can still be /interesting/ to work on.
3) If you just want to make enough money so that you can stop stressing out every single day of your worry-filled life over having to work yourself to the bone for the rest of your life/becoming homeless/being able to afford food/shelter/health insurance, and you think just about any startup can give you that Startup Lottery Ticket, you don't need to work on the next Stripe. You just need a couple of million, then you could move into your one room studio/log cabin/pod and live the rest of your life sans the typical day-to-day worries about the basics and be just fine. The diminishing marginal utility of money seems like an excellent bulwark against trying to do those Schleppier things. If you're going to make at least as much from a RecipeAggregator472 as you would from a Stripe, the choice is easy.
As pg states, undertaking these sorts of endeavors requires ignorance for some, but I would also add some other possible useful motivators (ignorance may also become tougher "motivator" since so much useful data about failure is so readily available):
1) The need for big money for other goals. If you want to be a mega-philanthropist/cure cancer/finally solve immortality/whatever, you probably need BIG BUCKS. The number of people motivated to actually do this (or who even think it is possible) is probably not very large.
2) Fanaticism. You want to make this project happen because it's just your dream. The rewards are irrelevant. You will make it so that it's possible to create coffee from rain no matter what it takes, it's just that important to you. Probably not that many of these either.
3) Revenge. Everyone told you it could not, can not, and will not be done. Maybe they told you that you will never be the Coffee From Rain King. Whatever the reason, you live to prove them wrong and rub their faces in it. You want to get on the news and blithely tell the world about you invented this genius thing while making no mention of your detractors, but you secretly giggle with glee since you know you were Right, and they were Wrong. This one might actually be the easiest of the bunch, but still requires a delicate balance of just enough ridicule and scorn to motivate one, but not so much so that one one thinks said thing is truly impossible.
4) Reinforcing the Peltzman effect. Certainly not a panacea either, but it could certainly help: http://www.angrybearblog.com/2012/01/peltzman-effect-why-eco...