Some people are lucky enough that they discover bitcoin when the value is too low and they buy more than 100 bitcoin but of course they sell it when the value is getting 5x of the original value. I think yes they hate what they did before but i think also there are some pioneer getting back and continue investing in bitcoin to make much higher income.
A lot of people who regretted at the time thought they were making the right decision because at the time, they would have made profit or cut their losses and whether it was a stupid or intelligent decision, they have been part of history and without their decisions I dont think we will have something to talk about. The same thing will happen to several of us who have some amount of bitcoin saved up and decide to sell simply because we thought we have either made enough profit or we are skeptical that the price will crash. The people of the future will then assume we made some foolish decisions but right now and now, its the best decision. Lets quit judging and saying they regret, its a gamble that played out wrong for them and hopefully they can live with it which is all that matters.