It's often a waste of time to get upset about things you can't change.
When your flight is delayed or you're stuck in bad traffic or it's raining on a day you wanted to go to the beach, that's the reality. Getting upset won't change things for the better (and I admit that I often make that mistake). The better job you can do of just accepting things you can't change, the better you'll feel and the less negative energy you'll waste.
There are about 40 colleges in the country where admission is absurdly competitive. The applicant pools are full of the most accomplished students in the world, and just about all of them get rejected. A lot of those rejected kids were just as qualified and worked just as hard as those who were admitted. It's neither rational nor fair. But it's the reality at those schools. You can complain about it or lament your admissions misfortune, but that's not going to make you feel better. And it's not going to improve your college outlook at all. You might as well accept it.
I'm not saying you should abandon your dreams if you think Princeton is the school for you. You can (and should) work as hard as you can to give yourself as many college options as possible.
But once you accept the admissions reality you can't change, you can put your mental energy to better use. You can learn as much as you can in your classes motivated by the fact that knowledge is always a good thing. You can enjoy your time on the soccer team or in the school play or at your part-time job because you know you're getting something good out of it even if Harvard says, "No." You won't take any rejections from highly selective colleges personally any more than you could blame yourself for not winning the lottery.
And maybe you'll even reject the notion that those 40 schools are inherently better than others (they aren't, by the way). You could take charge of your college process and find some other colleges that fit you well and that would be excited to have you join their class.
Sometimes acknowledging the reality actually leaves you with a lot more options.