My friends are stupid. Everyone I've ever known, currently know, or will ever know, is stupid. The answer is in three short words. People are stupid. This is my credo, my mantra, my First Law of the Universe.
People are stupid.
Think of everything you know, in every field imaginable, without the use of references. The best restaurants in New York City. Getting coffee stains out of a shirt. Now, think of everything you don't know, again without using any references. Again, assuming that you're sufficiently honest with yourself, the list of things you don't know will vastly outnumber the list of things you know.