Look at the adults around you. Half of them probably aren't as bright as you are, but just about every one of them knows a great deal more than you do. Life has taught them to cope, to compromise, to make adjustments, to find satisfaction in the possible. Those who didn't learn these survival skills live in small rooms with either bars or padded walls. School is a world of absolutes.
Life is lived in shades of gray.
What it teaches you is to do the best you can when you can, and then define the result in the best light. It teaches you that every problem is an opportunity to succeed - but that sometimes you don't. And that that's OK as long as you pick yourself up and move on. The future may in fact be yours, and maybe that will be OK, too. But for now, get a job, find a mate, raise some children, pay your taxes, help someone less fortunate, make a contribution to your community, focus on what matters and ignore what doesn't, deal with your own shortcoming and accept those of others, learn to give everything that's worth it your best shot - and manage to smile at the end of the day.