losing money is a natural thing to happen but it can be minimized by ourselves if we have good enough knowledge. in my opinion many people lose money in trading because it is caused by a lack of knowledge. besides that there are indeed many people who trade just to follow the trend but they do not have reasonable knowledge and I think this happens a lot.

besides that the second is because of the lack of discipline in finance. when they trade and there is no discipline in trading they can lose self-control so they spend quite a lot of money in trading.
besides that no one can predict market movements with certainty, so I think trading also involves luck even though good knowledge can help.