hehehe....i believe you specaulating you lost 20000$ worth BTC but thats not completely truth because back there that was just around 1000$ which equal 0.25BTC today. What if BTC today wouldnt be wort a penny would you care that you lost 5BTC in 2013? So leave the regrets behind and jump on BTC rocket! You might will have 20 x fold in value by 2021!
I get what you're saying, and everyone will eventually regret selling early. I think the best thing to do is to set a goal, sell when you hit the goal and be happy with it. I know whoever spent 10000BTC on pizza will be kicking themselves, but back then it would have been amazing to get free pizza! It's one of them things, but i'll set my goals, hold and sell when I know i'll be happy with the outcome!