I've repeatedly made the mistake (to the degree that it was a habit up until recently) of assuming the intent of other people, and adding matching caveats to my speech rather than giving the other person the opportunity to express themselves (or not). Asking questions and waiting for the answer, as long as it takes, even if it's uncomfortable, has been a change that feels healthy.

Another mistake I made is that for a year or so I replaced running with walking. I now do both again; running for one set of mental and physical benefits, and walking for a different set of mental and physical benefits. I expect I'll be back to a healthier weight in a few months, and less irritable within days. I'll also sleep better and not feel so restless and unused.

Third mistake: putting off finding a sense of purpose, and playing videogames for decades instead. The bar to engagement is so low with well-designed games that they provided a temporary sense of purpose that left me feeling hollow afterwards. It's not all bad, as these games (Diablo 1-3, WoW, and Hearthstone being the most compelling slots machines) may well have kept me away from other potentially-more-harmful escapes, and kept me even-keel enough to make it where I am today (a parent helping to raise our child, and someone who finally practices work-THEN-play rather than full-bore procrastination). I still play games, but a much smaller subset and almost entirely just with a couple close friends, as a way to stay in touch. I've sworn off all Blizzard games and most solo games. When I do get sucked in (most recently Slay the Spire, for a couple weeks), I see it for what it is, go along for the ride, and dismount & move on, appreciating the art and craft and not beating myself up for time I wasn't reading a book or going for a walk (though going for a wander in a less-familiar part of the woods pushes a lot of the buttons I like games for). Having a sense of purpose is important to me, and I actively pushed it away when I was younger because I conflated it with religion.