The thing about being an audodidact is that you can just stay in your comfort zone and never tackle anything beyond what you can easily handle. Contrast that to college where you absolutely have to learn new things and demonstrate your understanding of them to pass a course - a course you'll be taking with many other students, some of whom are almost certainly better prepared and more experienced than you. My first year of college was possibly the most humbling experience of my life because it showed me in no uncertain terms I that I didn't know shit.