I think there was a study that showed that Ivies, MIT, Stanford, etc. are really good at finding and admitting very talented, driven people.

However, that same study found that equally talented, driven people who chose to attend a less prestigious school did just as well in their careers as the people who went to the big name schools.

So there probably is a correlation between "I went to Harvard." and "I will be successful." But not necessarily causation.