I never regret on selling my bitcoins as whatever bitcoins I gave that are earned and not invested so whenever I m satisfied with the price I sell my bitcoins as I know that I can earn it back.
still no matter i have earned that bitcoin come from your own work not from your capital , selling bitcoin on low price where you can see higher price , it always be a big regret. it sounds like a BS when you feel nothing to see your 1 bitcoin supposed has $15,000 instead $150.
the point are you should never put the whole money to buy or sell it. save some for certain unexpected moment like ATH or the crash moment.
I sold btc many times and they were really cheap ones. Now I really regret for my trades in the past. I should have held them in my wallet for my better future, but I couldn't do this. Be patient for the success.