Main mistake about DCA IS that people don't sell when there is huge price swing.
There are other mistakes that someone commits when they're DCAing but you know what's with this? It's a very subjective thing.
Something might work for me and not for you and that's in general. That's why you may see it as the main mistake that others are doing but in reality, they really have no intention of selling because from their perspective this is what they do.
DCA to have more holdings which is they're considering for the long term.