Sequoia is not going to give $25 million away without good reason. It's just that folks like us can't see the good reason. Either the "good reason" is being hid from us for strategic reasons or Sequoia made a big mistake and the app/company is a dud.
Sorry, but this is really terrible logic. I have first-hand experience with watching VC's pour literally hundreds of millions of dollars into a company that I was certain was never going to make it (and which has since been sold off for pennies on the dollar). All along, people kept arguing that I must be missing something, because people wouldn't invest that kind of money unless success was assured.
I'm not saying that the "good reason" will result in a proven product. I'm just saying in their perspective they have good reason to spend that amount of money. And also it's Sequoia and they're not stupid.
