Some diet plans, notably Weighwatchers, depend on logging everything that is eaten, playing on the theory that if you have to log it, you may eat less.
One reason some people fail miserably in all attempts to control weight is because they become obsessed with food, and in the process realize they're hungry, and wind up eating, often what they shouldn't.
People "get religion" about some new diet plan. In their newfound zeal to implement it, they plan virtually bite by bite all the things they will be eating for some prescribed period of time into the future -- exactly this for breakfast, that for lunch, whatever for dinner, swearing off this comfort food and that junk food, resolving to snack only on sand, etc. Then they head to the store to stock up on all that stuff, sometimes inhaling a package of Little Debbies or Cheetos, enjoying "one last fling" while running the cart up and down the aisle, the surest sign that their project is doomed already.
It doesn't take long for people who are thinking day and night about what and when they are going to eat to fall off the wagon.
My contrasting belief has long been that successful dieting is more about what we don't eat, rather than what we do.
Sure, the excuse that's used is: "You've gotta eat something!" which is true, but if once in a while a person can just skip it, just forget about eating entirely, when trying to lose weight, he'll probably be better off than if trying to make frustratingly small portions, weighing them and going to all the trouble of figuring out the calories and writing them on a chart.
We eat so impulsively and so thoughtlessly sometimes that it's hard to avoid popping something yummy into our mouths just because the idea to do so occurs to us. Maybe an effective part of a solution is, when we catch ourselves doing that, to say: "Whoa! Not this time."