If I were to guess I will say that all of the people that lose money in the market did not made a serious effort to learn how to do it properly, there are those that never open a book about the topic and are the most obvious transgressors but there are many that read a book or two and begin to implement a method without even knowing what they are doing.

Why are they using indicator X instead of indicator Y? How they can calculate that indicator manually? Why are they using 3, 4, 5, or 10 indicators? Why are they entering or exiting the market? Is their strategy profitable? What is their ROI? How much they can expect to make in a year on average? I could keep throwing hundreds of questions and a trader that took the time to develop his strategy will know the answers to all of them while those that did not will not even understand some of the questions.