They (collectively) have thousands of employees, billions of dollars, and tons of things to play with (taste, texture, appearance, mouthfeel, snappiness, salt, sweet, sugar, packaging colours and styles, slogans, marketing, brand associations, shop placement, advertising) all you have is willpower to fight against 4 billion years of evolution telling you that fatty, sugary, energy dense food is important, and a whole pile of biases and weaknesses that you aren't really aware of and they are very aware of and trying to maximally take advantage of.