Paul Thomas Anderson is one of the more famous and successful film school dropouts, but the circumstances surrounding the way he left are pretty interesting. While he didn't have much interest going to school in the first place, and didn't have great grades in high school, he did eventually get into NYU, but with one foot already out the door by the time he got there, he came up with an interesting way to reassure himself that college was a complete waste of time.
While everyone has their own career path, and film school is a legitimate choice for many filmmakers, it's certainly not for everybody. Obviously there is a bit of subjectivity when it comes to writing -- and not everyone is a fan of Mamet -- but if you tried the test above during your education with a similar result, it could be time to reevaluate what your education is doing for you. It clearly worked out for Paul Thomas Anderson, but he didn't just quit film school and sit around, he knew exactly what he wanted to do -- make films -- and he did exactly that with the tuition money that probably would have been wasted at NYU.