The key is staying positive on the long term outlook. My brother sold half his bitcoin a month or two ago because he said he didn't wanna stress over it. I told him that was very stupid. He only had a bit over 1 bitcoin anyways, so even if he lost all the money its not like he'll miss it in the long run, but if he had stayed positive he might be sitting on well over $100k in a few years. Just gotta keep a positive long term outlook. Sure it sucks getting trades stuck for a few months or watching your portfolio go down for a few months. But if you wait long enough 99% change you'll be making lots of money again in the relatively near future.
Staying positive may be good if you wanted to focus on long-term investments - in fact it looks like the only option to stay just sane in the long run - but this is not what I wanted to say in OP. It is not about talking yourself into doing nothing for a couple of years in a less stressful way. Quite the contrary, my whole point was about carrying out a well-thought-out plan how to get out of losses if you were unlucky to buy at December highs.