The most important revelation I ever had about existing and being human was the understanding that our brains are not machines of logic and reason, despite being capable of performing logical reasoning.

The brain is, by default, a story telling machine. It just takes your memories and experiences and uses those things to explain whatever you're feeling at the moment. Those explanations don't necessarily have to make sense or be connected to reality, it just has this massive priority to weave a coherent story to explain how you got here, feeling this thing, doing whatever it is you're doing.

In the early world of survival, this helped us. Seeing paw prints by your watering hole made you feel uneasy, your brain tied that to the time a saber-tooth cat killed your uncle. Emotional connection to a sense, an association, a story for why you should feel afraid.

In the modern world, the brain tries to do the same goddamn thing when someone you like ignores you or when you feel embarrassed in a social setting. Small things that spark the same survival response to weave a story together around it. Or you feel a sad spell from a chemical imbalance and instead of waiting for it to pass, your brain decides it's because of your entire life, the people around you, and your lack of success.

From that understanding, you can beat rumination, you can challenge yourself, you can overcome addiction and do a lot of amazing things with your life, but it all comes back to understanding that your brain doesn't work "out of the box" and if you want to make better decisions and feel better, you have to manually TRAIN IT to make you feel better and make better choices. You have to learn to control not your emotions, but your reactions to those emotions, to think through your thinking, to follow your chains of thought to a source. This is what a good therapist will do for you, set you on a course to retrain your brain.

A lot of people resist this because it feels "fake" and that you're "fooling yourself," so they resist change and training their own brains.

You are not your brain. Your brain however is very, very complex, with a multitude of voices inside of it each trying to get attention, you're only aware of the top-most surface level that uses language to think, but the very best thing you can do for yourself is get in the habit of thinking about how you think.