M8, it is lack of experience and your attention. That's all. If you want to be really successful trader, you should not only buy and sell, but also doing your own research: how the market rises and falls, how to buy cheaper and sell more expensive, how to use various types of orders, how to operate on various exchanges. Only in this case you will bu sure in your investment, and woun't do stupid mistakes. Trading is a job and you should pay a lot attention for it. 
yes we already know that but all of that is useless if you are not lucky . luck is all we need so that we can buy or sell more efficiently because we cant predict on what will be the next move of cryptos . trading/investing is more of a kind of gambling because all works in random here though in gambling the chances of loosing more higher than winning because we dont have a reference or a sign , not unlike to trading and investing where we can follow or listen to our own instincts based on what we see or hear in the news .