I feel pretty confident in saying everyone has the thought at some point in their life that they are not enough. In the words of Brooke Davis, "That's what I'm of... Not being enough. Not good enough. Not smart enough. Not pretty enough." I'm not sure why every single person on the Earth feels this way - each person for a different reason. But, it's something that whether it crosses someone's mind every day or once every 10 years, it is still there. Everyone feels it. And to be honest, it's something that needs to stop.
If you feel that you are not enough to another individual, you can either sit there and sulk or you can prove them wrong. If it's a parent that feels that you don't do well enough in school, study your hardest, get your good grades and prove to them that you're crushing it. If it's an individual you might be dating, first off, dump them. Second off, show them everything they're missing after you left them by being all that you can be.
If you feel you're not enough because you didn't get a job or get a promotion or a position in a club you really wanted, it's not because you're not enough. Being an "adult" and having a job is like playing a game. You have to say all of the right things, do all of the right things, prove to the right people that you're the perfect fit for this position, and let me tell you, 99% of people fail at playing that game. You have to have so many cards align in order to be next up in getting promoted or land the dream job or become president of the club on campus, and if it doesn't work out, that's okay.
Let me tell you the secret to being enough in all of these examples in which people constantly are kicking themselves that they "aren't good enough." Ready?
You have to be good enough for you. If you know you work your hardest, study your hardest, try your hardest, love your hardest, are the kindest, most genuine person you know how to be, then you are more than enough. You have to be able to look in the mirror and say to the person staring back, "Hey, I'm proud of who you are/the work you did/how far you've come," and you've won the game that everyone else is trying to prove they're winning at.
Love yourself. Be good enough for you because news flash: you are enough.