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.
I think your mentality going into a highly volatile investment like Bitcoin has to be "hey there may be times when I'm way down on my investment but I believe in it long term and I only put in what I can afford to keep in there for a long time so I don't care about a market crash, I can just wait".
If you don't have that mentality and strategy then you shouldn't be investing in Bitcoin. That's how you stay positive no matter what the price.
My parents and uncle finally decided to buy around $10k/$11k in december, and bought more way up at $17k. But I told them when they were buying to just make sure not to sell if the market crashes, hold out for the long term as they can be highly confident it will be up at some point in the future even if they've lost value for a while. The long term view is how you not care about what the price is at any given time.