IMO, education or lack there of. It's commonly known that we (speaking generally) underestimate the caloric content of food.
A really big problem is chain restaurants.
Ex.
You go to O'Charleys and get the Pecan Chicken Tender Salad. You're thinking, "hey, it's a salad, it MUST be healthy". Yeah, if 1020 cals BEFORE any dressing is considered low calorie these days. A Big Mac and order of medium fries from McDonald's would save you 100 cals.
Another problem is overestimating the caloric expenditure of exercise.
Say I'm a 180 lb man. If I walk (20 min miles or 3mph) for an hour, I will burn (roughly) 300 cals. Look….I just burned off (almost) 1/3 of lunch. But wait, I forgot that I would've burned 100 (roughly) cals sitting my (lazy) rear on the sofa watching reruns, so I only really burned 200 cals (as a result of the walk vs sitting).




