David Liu is a technology entrepreneur in San Francisco. He has helped found several start-ups to market products he has developed, including those stylus pens the UPS driver hands you to sign for your packages. But even as he dreams up new inventions, an ongoing patter in his head objects that they are stupidly obvious. And despite his accomplishments, Liu teeters on a mental precipice: “It feels shameful, like, hey, I’m in my early 30s, I should have had a Yahoo by now—or I should at least have had a company I sold for tons of money.”