I think everyone who has dabbled with crypto currencies for a few years has at least one painful story like that. I sold all my ETH at 16 or 17 dollar a piece after the developers did the hard fork to steal back money from the DAO hacker, I really thought ETH would die because of that. Well, turns out it didn't die. While I could have made thousands of dollars selling my ETH now compared to the few hundred dollars I got back then, I still think it was the right choice at the time (and I made good use of the money).

I think that is the best way to think about it. I didn't make that choice in a vacuum, there was a reason I sold, I thought long about it. I also once owned 35 Bitcoin and sold them for about $100 (Spent would be the better word here than sold, I actually used Bitcoin to buy stuff, I didn't use it as an investment). Quite painful to realize how much money I'd have now if I I had held on to them. But again, at the time, the decision to spend the Bitcoin made sense, so it was kind of bad luck and not a mistake that I could have prevented, it only looks that way in hindsight, so it's nothing to keep fretting about forever.

Berating yourself only makes sense if you actually had access to information that would have changed your decision and didn't make use of that information. Otherwise, you made the best possible choice with the data you had on hand and that's not a mistake, even when it turns out you were wrong.

I've got one story like that too though, one that truly was a really stupid mistake. I sold 100 LTC for $1. In total, not per LTC. Selling for $1 is just stupid. I obviously didn't need $1 so badly that I had to sell, I could have just held on to them, there is no excuse for that particular bit of stupidity :)