There's also a different 100 hour rule. 100 hours is enough time for someone to become dangerously competent: just competent enough to complete something, but not competent enough to complete it well.
"This survival guide for new pilots identifies the pitfalls waiting inside the killing zone, the period from 50 to 350 flight hours when they leave their instructors behind and fly as pilot in command for the first time. Although they're privately certified, many of these unseasoned aviators are unaware of the potential accidents that lie ahead while trying to build decision-making skills on their own -- many times falling victim to inexperience."
I'm definitely going to pick up that book.