I not certain, honestly. Everyone who claims to have any understanding on the subject seems to have a slightly different opinion. I personally haven't been able to form a firm enough understanding myself and can't say what's missing.

My opinion at this point though is that the following are possible causes to a lack of success:

• Lack of effort / intent in developing skills required
• Incorrect technical execution
• Incapable of developed skills required no matter how much effort

I'm curious to hear your feedback / thoughts?