The #1 reason why most people lose money in trading is:

Their desire to be RIGHT is greater than their desire to make money.

It means you took a position & you are smart enough to know where you are wrong and should exit, but being right was so important to you that you held.

Other leading reasons...

A lack of risk mgmt, lack of discipline, lack of a plan, lack of following YOUR plan, thinking SOMEONE "knows" what will happen, following moonboys, following magic price models, following fake TA gurus.