Being profitable over the long term is more difficult than people realize, and the main reason is risk. There is one phrase that has stuck with me, which says something along these lines:
The secret to long-term wealth is not managing profit but managing risk.
That means that if you focus on the profit potential without understanding the risk potential, you will lose money, guaranteed.
Understanding risk is a complex topic by itself. But there are many topics out there to get you started. You have to put in the time and effort though.
I’ve made a Getting started tips post, this could be helpful for you, specifically point #3. If you can give us more background about you and your goals, we will be able to give you better answers.