If someone sells and then buys more at a lower price and then uses it to invest, then they are not actually planning their investment correctly. Rather, they are relying on market speculation. No one knows whether the price will really fall. Many times, after selling in the hope of making a profit, the price does not come down and goes up. Then you have to enter the market with less Bitcoin than before or you have to sit around. This changes the basic concept of investment. The main strength of investment is time, patience, discretionary income, and regular savings.
Well a trader will never ask themselves this question, sure they are going to regret selling immediately but that because they would hope they had sold after the price went up again and I'm saying again because I'm assuming that the first time they sold they believe it was at a profit which is probably also true since they sold higher then what they bought.
But an investor would not have sold, they would have instead kept buying more and the price of bitcoin climbing higher would have been even more motivation for them to keep buying.
So while traders sell too early only to sometimes regret that sale an investor see reason to buy even more.