When I met with my personal trainer (Joyce), the first thing we did was to sit down and discuss my goals and needs. She asked me a few questions and then asked, "So what has been the obstacle to your losing weight?"
I explained that in fact I had lost about 55 pounds over the past three years, so I haven't faced an insurmountable obstacle.
She asked me about my diet, and I explained that, when I am on plan, my diet is very healthy - low-fat, lots of fruits and vegetables, plenty of fiber, etc. - but that I am sometimes not on plan and then I don't eat as well.
She said something like, "So you sabotage yourself?"
It seems likely that some people do sabotage their efforts in various areas, out of perhaps a feeling of not deserving success, or fear of reaching their goals, but in general, I think it's less widespread than people think. I really do not believe that I subconsciously sabotage my dieting efforts, and in general, I think the belief that losing weight would be easy if not for dsyfunctional psychological factors is wrong.
What I told Joyce is that I don't think I sabotage myself; I think I just prefer eating unhealthy things in large quantities to eating healthy things in small quantities. And I think this is basically natural.
From one perspective, it is well known that people discount the future in favor of the present. If you offer people a choice of fruit or potato chips today, they'll chooes the potato chips, though if you offer them the same choice for a week hence, they'll choose the fruit. People are generally just unwilling to take a loss today in order to have some gain in the uncertain future.
But specifically relating to food, I have a different perspective, which is that my body (including my brain) evolved to keep me alive and help me make babies. And in our evolutionary context, it would never have made sense to pass up available food, or exercise our bodies unnecessarily. Doing something like that is crazy, and if you take it into your head to do it anyway, you ought to have some very strong built-in mechanisms to keep you from succeeding.
It is definitely possible to outwit our internal mechanisms and succeed at losing weight, and I don't think it requires strong will-power (which I don't have, so I guess it's convenient that I think that), but it requires persistent attention. And I don't think the psychology that acts against it is intrinsically dysfunctional, unhealthy, or unusual.