If your coins are sold, it means only that you created a order for sale. The coins themselves could not sell themselves. And this is not a matter of luck.
I think you need to deal with the subtleties of the exchange on which you work. There is probability that you are trading in the margin trading section, and you don't realize it. I met several people who traded with margin, but they were confident that they were just trading on the exchange. Then the only thing that helped them to understand, is that from their accounts periodically disappeared currencies.