The Launch Pad Inside Y Combinator, Silicon Valley's Most Exclusive School for Startups
Randall E. Stross
Try and pick things where the cost of failure is low and the cost for you is basically time.
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You want to work on something where if you see it among your friends and family, they go out of their way to go and tell people about it. Because friends will use stuff because they're friends, right? But the true test is if they start bringing other people into it. And that’s something that they won't do out of obligation to you.