I think I am happiest when I can accept everything: who I am, the circumstances I am in, the way I treat others and the way I am treated, and the direction in which my life is heading. This idea is nothing new, but sometimes I forget about it, despite its simplicity.
Thinking about acceptance helps me separate the things I want to live with from the things that I don't.
For me to be happy, I don't need all of my personal circumstances to be positive, or even going "my way". In fact, I am happier when I realise that I can accept and live with unchangeable things that aren't good. The sense of pleasure comes from knowing that everything won't go my way, and being happy in spite of, or perhaps because of, that fact.
The things that make me unhappy are the things I can't accept, and yet can change. I think the discomfort comes from knowing that I want to and can control something, but that I'm not taking any action. I can hear myself, internally or externally, making excuses; that I'd love to be able to feel differently or behave differently, but I can't, or I don't have the power to. The second that one of these thoughts enters my brain, I'm aware that I'm lying, and letting myself down.
I am a pretty happy person, and I think this is because there aren't many things that I lie to myself about, and I find myself accepting of most things. I really want there to be nothing changeable that I want to alter, but won't. But at the same time, I think like having flaws sometimes, and I don't want to be mentally unblemished and perfect.