From my experience, here are 4 reasons I discovered:

1/ Lack of Discipline— a) Not sticking to one strategy, b) not respecting your trading rules, c) not sticking to your plan.

2/ Lack of knowledge—Inadequate understanding of the market, trading strategy, financial instruments, and fundamentals can lead to poor decision-making.

3/ Not having a mechanical trading system—This leads to emotional trading. Decisions driven by emotions like fear and greed rather than rational analysis result in significant losses.

4/ Overtrading—Taking many trades will affect your decision-making ability and lead to poor decisions.

If there are other reasons why traders lose money, share them with me.