Something I've recently learned about my thought process:
My mind is constantly drifting from thoughts of the past ("If i had done that differently, how might things have gone?")... to thoughts of the future (If I do this, what might the consequence(s) be, and how will that affect my life?"). The future-based thoughts tend to consume the majority of my focus and energy. This prevents me from being able to fully enjoy the present, which is a key to finding happiness and contentment. (They call this practice of being in the present: "Mindfulness"... something I've begun to explore for myself.)
It's funny because I've always felt time itself is just a man-made concept. The past is gone, never to visit us again. The future hasn't happened yet and is constantly in a state of flux, so the future, in a sense, doesn't exist either. One could even argue that the present doesn't even exist... because by the time you identify a moment as being "the present", it has already escaped and become the past. So my mind often feels conflicted about things. This confliction inevitably leads to frustration. The frustration becomes anger... at the world... at society... but mostly just at myself for not being smart enough to figure these things out and make sense of them.
^^^ This is a good example of why I'm in therapy in the first place.