Having spent time in biology, being CEO of Google is a way more realistic goal than curing cancer. As far as the moon, I grew up on Star Trek and the idea of spending my life in space and seeing new things was absolutely what I wanted. But once I found that Earth contained a lot of utterly fascinating people, being able to meet them mattered more to me than spending a shitload of time getting as far away from them as possible to do a fairly small amount of rock collection - I'm going to be exposed to more new ideas staying here than I am up there.

But it's a fair point! Our aspirational goals are influenced by what we believe is possible, and that's amazingly contextual. What we're lead to believe is possible changes what we believe should be possible for us, and that changes the standards we set for ourselves.