Well, most of us actually got stuck in our HODL mentality but not like the future is dead and we sure do know there is a lot to experience later on positively. It is either you are long term investor or a trader and if you are trader, I am sure you or the OP would not even be stating this.

My point is there is no need regretting a moment you obviously cannot change but rather find ways to make amendments; which to me, would make sense buying at the dip when you feel there is enough room for the market to move upward later on, so you do not end up regretting not buying the dips later on.

Not everyone can be a trader, you could have sold, and the market kept moving up. This is real market and not knowing how to trade makes you a gambler if you make attempts on the market, so for me, it is either you learn how to do well as an investor or you learn how to do well as a trader than regretting moments you cannot change.