Well thats just stupid. I took out a big loan to buy a bunch of bitcoin in late october just before the price went nuts. It was a fantastic investment. But I didn't take out more than I could afford to pay off. If anyone really did take out loans that were so big that they can't afford to pay the monthly payments without selling their investment thats just stupid no matter the market.
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.
There is absolutely nothing wrong with selling your investment, especially in a bubble situation.
But if you are selling because your emotions in a falling market(and everyone experiences that, by the way) are telling you that you should just get out of bitcoin for good, then that's where the mistake is made. What will usually happen is that you'll sell at a low level, like your brother, and then have the fear of missing out when bitcoin takes off again in a bull market, so you're actually losing money that way.
It's not about staying positive all the time even if bitcoin's in a huge bubble, but it's believing in the long term of your investment in BTC. After all, you invested because you think that BTC prices can really go up over the long run and if you sell now, you're missing that opportunity entirely.