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.
Based on my personal experience, losing money in trading is mostly due to greediness, most traders have the required technical knowledge of trading but they still lose large sums of money in various trades. I believe if one can be very content with profits no matter how small they could be, losses can be vastly minimized.
I have learned the habit of taking profits, and it has been working for me so far.