I think just because it is an "extremely tough thing to do" doesn't mean that people shouldn't do it. Sure, people who aren't capable of coming up with a brilliant idea shouldn't do it, but those that are exceptional are better off thinking about the next big idea than a small one.

I think its more of a blanket statement to save those who aren't "exceptional" but are just good-very good. If you're good-very good, then yeah stick to the smaller ideas instead of daydreaming about creating the next Microsoft, Apple, Google. Its tough to say, but some people are just better than others. Some people are great. The few that are "great", for the most part, are the ones who will create the next huge thing.