I made a mistake several years ago to sell a bunch of Bitcoins for $28,- each. Early 2013. Only a few dollars profit. Bought it much higher few years later but never sold again 
There is always a mistake that one will have to make before getting to know how things are done with trading in crypto currency.
I sold an altcoins which I had, which I have held for some months, when I sold them all, the next two days the price incresed to 0.5BTC. So, it just happens.
I didn't regret in anyway.