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.