To emphasize the rational in my reply: I challenge you by saying the above claim is not true. Dieting for a day or a week or a month with no results is possible (and frustrating). Dieting for two years "with no results" means either a rare medical condition (seek help from a professional) or, more likely, you are dieting incorrectly and refraining from rationally noting this fact and trying to be less wrong.

Yes, I can specify better. I have tried several low-calories and low-carb diets, usually for a period rangin from one-month to three-months. The best result overall has been to lose 2 kgs (that would be 5 pounds), which were regained a couple of weeks later.
It's almost trivially true that I'm dieting incorrectly, but unfortunately the scale doesn't tell me what I'm doing wrong. It just tells me that I'm doing wrong. I lack the incremental feedback that would allow me to correct my course. So the only thing I could do was changing the diet altogether.

You can eat optimally and be unhealthy if you do not excercise minimally.

I was under the impression that studies have shown that exercise has almost no influence on losing fat, but I'm possibly mistaken.