Obsess About the Quality of the Product
Sam Altman originally founded Loopt in 2005, before selling it to Green Dot for $43M in 2012. He's now a part-time partner at Y Combinator. In addition to this quote, he's also got a bunch more excellent startup advice on his blog.
"Obsess about the quality of the product."
Who Said It?
Sam Altman, Y Combinator