That's exactly the point. Google didn't start with that mission, it had to be refined. And Google, meaning Larry and Sergey working on algo's prior to actually starting a commercial entity. The parent's point is that many of the most successful tech investments have come from businesses that are generally dismissed as toys in their initial phases. YC invests in companies at their earliest stage, so it seems odd that the mission statement needs to be so well refined. This invariably means there's a disconnect between what pg has traditionally said and what sama is dictating now.

> Don't be discouraged if what you produce initially is something other people dismiss as a toy. In fact, that's a good sign. That's probably why everyone else has been overlooking the idea. The first microcomputers were dismissed as toys. And the first planes, and the first cars. At this point, when someone comes to us with something that users like but that we could envision forum trolls dismissing as a toy, it makes us especially likely to invest.

http://paulgraham.com/organic.html

Anyway, I think the reason that sama says this is because it is absolutely essentially for a company to get big, but that doesn't mean they need to have it right away. Also, let's be fair, determining something that is clear and important is very subjective.