The transition from youth to adulthood can be smooth or incredibly difficult. What is the most important lesson you learned since middle school, and how has it guided you?
The most important lesson I've learned since middle school is that it doesn't matter how driven you are, how smart you are, or how open you are to learning and working. The only thing that ultimately matters in life is skill and not knowledge. Knowledge is not power, but is usually useless in of itself and can only moderately enhance skill. Furthermore, while skill can be developed, the proficiency of skill is almost always dependent upon innate, immutable talent, not the hours of work you put into studying and practice.
In other words, going to school and pouring yourself into your studies and extracurricular activities (other than athletics) is a one-way ticket to poverty. The only way you can get ahead is if you are already gifted at a rare skill, can produce on a consistent basis, and are lucky enough to get noticed. However, if you are like 99.9% of the population, then you might as well do the best you can while in school -- at least then you can point to one time in your life that you are not a failure.