Your assumption that everyone has made such mistake is very wrong there are lot of people here in this forum who still holds Bitcoin since when bought about a more or less 10 years ago but haven't sold they Bitcoin due to a well planned investment strategy.
Don't mean to say everything but I'm sure they must have sold a bit of their holdings and they did. But the most important thing is not to sell everything because that will make them frustrated when they see prices continue to rise.
Most people whom are selling for some reasons such as personal issues are likely due to lack of proper planning, it also advised to invest what cannot in anyway affect your standard/cost of living i.e make reservations of extra funds for emergency situations etc to be well prepared for investment.
Some people just wake up and use almost all they have to invest in a business (investment) and when something goes the opposite of their expectations everything crashes all because of lack of planning if you have been reading through this thread you will find out what is required before going into investment. so not everyone is victim of selling their Bitcoin real quick because the have a well planned investment strategy.
So, for those who trade, of course they are not investors who implement long-term investments. And I have said before that they are daily profit seekers and they can do it several times every day. they only focus on analyzing charts when it is time to buy and sell.
Trading Bitcoin is equally gambling and those who gambling stand a chance of 50-50 with it either they loss or win.
Of course 50/50 and I would not call this a form of gambling because if they are good at analyzing charts of course they are able to achieve a lot of profit because they can minimize losses with the patterns they have in buying and selling.