Given a same method and same set of guidelines for selecting trades and managing them, some traders go on and do very well, while some traders do very badly. Given same mix of methods discussed here or in any book some traders will go on and make high returns using them and some traders will make losses. So is the issue with method or a trader.
Now this is not an issue with trading only. In all fields involving high degree of personal skills and judgment, this is a common phenomenon. I worked for six years in advertising. It is one industry where either people understand it and are very good at it or just don't get it. The feel for producing, judging and executing good advertising is very unique skill. The methods used are common knowledge , but you will find many people spend years in the industry and never develop the ability to judge or produce good advertising. Similarly good marketers have an intuitive feel for marketing and that is why they are so much in demand. With so many marketing courses around all marketing theory and methods not being secret, why is this so. In most fields most methods are not secret but ability of people to internalize those methods and execute them is where you will find a gap.
Most people do not explore the reason for this or are not aware of the processes that go through in the mind which can help or hinder this process. If you want to improve your trading results, it is an area to explore.