The biggest mistake that day traders make (especially crypto day traders) is believing that they have an edge over everyone else because of the charts they look at. The biggest mistake is not believing that day trading is 100% gambling, because that is exactly what it is. The only way to consistently make money over the long term is to invest based on value and fundamentals.
I totally agree with that
I don't know why you think that day traders believe that they have an edge over the rest of the pack. I for one don't feel like that. I'm a day trader in some assets and a long-term holder in other assets. Though I agree that short-term trading is mostly gambling unless you know what you are doing. But this is the whole point of this thread.
It is gambling even if you say that you know what you are doing. Your above example isnt a good one for me:
For example, you buy a few bitcoins at a December high and expect the price to continue rising, which is kind of obvious. Instead, the price starts crashing down and you find yourself in a situation that you didn't envisage or consider beforehand. So your best option would be to bring things back where they were as fast as possible even if it means some loss.
As a long-term holder, I just HODL. That saves me a lot of headaches and a lot of trading commissions. You just put an example of what newbies do: to buy after the last ath out of FOMO and to sell after the dip out of panic. This is the opposite of what I usually recommend