The purpose of going to school is to learn; getting an A is the indicator of success (but can be falsely attained by cheating). The purpose of life is to grow; being happy with your life is an indicator that you're succeeding (but can be falsely attained by addictive behaviors and substances).
https://yourmeaninginlife.com/blog/happiness-without-growth-is-like-getting-an-a-without-learning
You can always find a reason to complain, and you can always find a reason to be grateful. The former will lead to a miserable life; the latter will lead to a more pleasant life.
https://yourmeaninginlife.com/blog/it-will-always-be-something
There are many misconceptions about how important growth is to your life, from what kinds of growth are possible, whose growth is meaningful, and how growth is meaningful even in the face of endings and death.
https://yourmeaninginlife.com/blog/misconceptions-about-growth-oriented-meaning