Comment by program_whiz

Are you asking why people can't seem to stop? Or why you seem to possess that ability? Both are biologically mechanistic like all behavior. Probably similar to why some people will kill for heroine while many don't. Or maybe the same reason your gut bacteria can process certain foods others would die from (peanuts), it's environment plus biology in a complex set of local minima that cause repeated behaviors. Is it surprising a biological system optimized to gorge sugary food as late as 200 years ago struggles to stop now? You may have well starved if you ate just one helping while food was available, discipline around food would be a fools pursuit (like intentionally drinking less water than your fill at an oasis).