So here's the subjective rundown. We eat mindlessly most of the time. Why? Because we are on autopilot.
But also because it is cultural in the west. People in the east (Japan, for example), eat to 'not feel hungry'. Westerners (Canada, U.S., for example), eat until we 'feel full'. As a result, getting fat, or eating too much is much easier for us than we care to think.
A big plate will trick you into eating more. More variety, such as different coloured M&M's will make you eat more (think buffet, you just 'need' to try everything). Even a bowl that fills itself, without you knowing, will make you eat more.
But to really show how dumb we are, do this. Take 2 bottles of the exact same wine, same age, same everything. But switch out the labels. One from California, and one from Detroit. Suddenly, the California wine 'tastes' better, in all tests with real people. As well, the drinkers believe their food tastes better, and they even stay longer to enjoy their meal. Rinse repeat with name brands from shoes, ketchup, and everything else on the market.
Now for fast-food, such as a bowl of chips, place it next to you, and you will pig out. Place it just a meter away, and you will eat a less. Place it 2 meters away, and suddenly it's too much effort to eat. We don't want to consume energy to get energy. This goes as deep as Risk vs reward, when a field mouse needs to run across a field to get a berry, while the watchful hawk preys on the mouse.
Oh, and manliness vs. being a woman. Men believe it's manly to eat a lot, especially on a first date, while women believe they should eat only a little, to be perceived as feminine. Not to mention, eating meats is more manly as well (despite the huge negative health issues with eating beef).
Then we have scientifically manufactured colours, tastes, and smells, which culminates into McDonalds and any other fast-food on the market. Each food is engineered to have the scientifically 'optimal' amount of the trifecta: salts, fats, and sugars. The trifecta feeds back into our primitive monkey selves, when food was scarce and dangerous to consume. Salts help us store water, fats help us store energy, and sugars told us that a food was safe for consumption... as opposed to a sour poisonous berry.
Food inheritance was interesting as well. Why do you hate that food? Why do you love it? Can you trace it back? Dig deep. Dig into your childhood when you first fell in love with that taste, or the process of getting to that food. Does it remind you of your parents, your friends, relatives, that special occasion? We associate our emotions to certain foods, plain and simple.
Finally, Subway sandwiches has been lying to you. Sure it might seem healthy, but is it really? How many calories are you actually consuming? Not too many less than a McDonalds big mac. Add all that sauce, meat, veggies, bread, a drink, chips, and a cookie, and you are eating maybe 1000 calories? Om nom nom, no thank you weight-loss Jared.
Common sense? Not when you eat with your stomach, and not with your head. Also, those low-fat variety foods are only fractionally low fat. But you also end up eating more of the low fat variety... you just tricked yourself.
Nonetheless, be MINDFUL of what you eat, but before you are, read this book. And if you are a fat shit, hit the gym ;) True story.