Inability to follow a profitable system is probably caused by lack of capital and/or lack of trust in the system. The latter can be overcome by understanding what the system is based on and thorough testing. The former by not trading until sufficient capital is available or by willpower. Another possible reason could be bad execution - things like not running the system in time, not updating data, not giving the orders in a timely manner. This one can correct by willpower as well. When I used a system once upon a time I tested it thoroughly before starting actual trading and then didn't follow it properly due to fear of losing caused by undercapitalization. The way the mind works - mine at least - seems to result in underperformance when not taking all system signals but picking them. This dawned on me and I took care to get the system signals only and blocked other influences like looking at charts, watching market tv, reading newsletters. I then forced myself to take all signals despite undercapitalization and became successful with it. Experts maybe wouldn't approve of that but they have different interests than moi, like selling books or keeping clients etc.. My risk, my decision, my result. Helpful to me was also understanding that successfully applying a system is a process which takes a lot of time. This process consists of many small steps - the individual trades. Over time the positive expectancy would show in profitability but it is still a process. And I need to allow it to unfold and not stand in the way. Also, one should be aware that there are no guarantees for success, no sure things. At least not to my knowledge. If one can't accept that then trading is quite difficult. Every level of success is possible but nothing is guaranteed. Trading a system is a business decision.