Perspective and context are extremely powerful factors in our perception of life. If you grow up poor, a middle class life seems "rich". If you grow up rich, a middle class life seems poor. On an intellectual level and in gross generalizations, such as the absurd situations that play out in movies or television, we understand this clearly. On a personal level, we fail to internalize or even comprehend it.
If you grew up receiving an allowance from your parents of $10 a day, your perspective about money would be different than if you got a dollar a day. A child with $10 per day to spend would be able to buy pretty much any toy, candy, or experience he or she might want either immediately or by saving for a short time. A child who got a dollar a day would view things rather differently. All things would come more slowly to such a child and the value of rewards, when they came, would be viewed as far greater compared to the child with the more lavish allowance.
Scarcity builds a different context for rewards and perspective affects how fortunate or blessed we feel. This applies to everything, but people tend to objectify such things much better when money is the topic at hand. Since most people understand money in concrete terms, "wealth" is something we can all identify with as a factor which can distort perspective. We think people with too much of it are spoiled and don't understand what it's like to live like "normal folks". Trying to help people see food from this same perspective is an order or two of magnitude harder. The reason for this is that "food wealth" is so common and harder to objectify.
One thing that I realized when I started modifying my behavior was that I was indulging in food like a super rich person indulges in jewelry. I felt it was normal and natural to eat what I ate because it was what I always had access to and could eat. Part of this was the patterns my parents foisted on me, but a lot of it was also cultural. Americans don't open a packet of Oreos and eat one or two cookies. They eat half or all of a sleeve. Americans don't order a small pizza and eat one or two pieces. They order a giant one and eat 4 or 5 of them. If they have one slice, it's an enormous one about the size of an entire small pizza.
Changing the context within which we view food is a challenge because of personal psychology, upbringing and culture. It's naive to believe that cultural forces do not come to bear on those who attempt to modify the scale of their eating. When I tried to change my eating when I was in high school, my father mocked and made fun of me for trying to more slowly nibble a potato chip so that I experienced it more. Many people who go out to lunch or dinner with coworkers are pressured to consume more and if they eat small portions, others remark on what they are doing. Such comments may range from accusing you of having some sort of eating disorder to saying that the person making the remark couldn't get by eating "so little". Though it is not the intention, the message is clear, 'you are acting outside of the norm, and it makes me uncomfortable.'
As difficult as the cultural pressures can be, personal ones are far harder. Our own idea of what is "enough" is very difficult to battle, and it's one that I've fought with for the last two years and have only finally wrestled to the mat in the past several months. I'm talking about the part of you that eats a cookie and it tastes so good that you want another and then another. That part has been diminishing in me for quite some time, but it hadn't fully been laid to rest until recently. Now, I rarely have interest in "another" after I've had one of a treat. My problem now, when the inclination to eat a lot hits (which fortunately isn't too often) has stretched out to a desire to sample small amounts of many things from nibbles of cheese, to chips, to cookies, to chocolate, to bits of meat, to olives. A cornucopia of bites generally doesn't add up to much, fortunately, so I can "get away with it", and I consider it a better "binge" than wanting to eat an entire bag of something, but it's still not where I want to be.
One thing I realized is that going from the food equivalent of $10 a day to $1 a day makes one feel impoverished on the food front. If you are accustomed to eating all of the cookies you want, then limit yourself to one, it feels like deprivation. If you grew up without an allowance and one day started getting a dollar a day, it'd feel like wealth. Back in the past, when food wasn't as plentiful and convenient, people who got a cookie once a week were delighted because they weren't used to having them anytime and everywhere.
The issue for most people isn't conceptualizing that they'd be better off with the food equivalent of a dollar a day. The problem is putting themselves on that budget. And note that I use a cookie as a convenient thumbnail for any food. The problem could be eating too much fruit, cheese, or whole wheat bread. You can overeat on any food. It doesn't have to be unhealthy or "fun" food. The point remains the same.
My point is that we see food as something like a bank of infinite funds. We don't budget because we don't have to. We're the kids with the big allowance having fun because there's no reason not to... at least not until something happens and we find out that we can't touch that money anymore. In the case of many fat people, that is health or mobility issues. It's like being super rich with a penchant for bling and finding out that you suddenly are allergic to all precious metals and gems and now you can't shop for jewelry anymore.
For me, one of the turning points was internalizing the fact that food wasn't something which I could indulge in in an unlimited fashion. The limit used to be what my stomach would hold (and even then I'd eat until I felt uncomfortable a lot of the time), but I had to understand that the limit was somewhat less than what my body could burn in a given day. People know this rationally, but they act irrationally. They tell themselves they need that metaphorical $10 a day and can't possibly live on any less despite ample evidence that plenty of people live fine on a (again, metaphorical) $1 without keeling over from malnutrition. We convince ourselves we "need" more food than we really do, and what is worse, we believe that we can't possibly be "overspending" if all we are overeating is "healthy" food. You can be fat on anything, including fruit, oatmeal and yogurt. You only need so much of anything to be healthy, but we're convinced otherwise.
I think the reason people have such a hard time losing weight is that they try to go from one extreme to another. If you think about this with money, again, it is easier to understand. Going from $10 to $1 is very hard. Going from $10 to $9 a day sounds doable. This is what I recommend people do in regards to food (hence my initial advice to eat two tablespoons less and drink slightly smaller amounts of caloric liquids at first), but the results aren't fast enough for most people so they move too far too fast without making the proper mental adjustments or allowing their body to acclimate. They then proclaim that all has failed and go back to their more expensive lifestyle (or more).
The thing is that we can get by with less food than we think just as those who live in wealth can get by with less money. It's all about slowly developing a different context and perspective rather than rigidly sticking to the current one and claiming that change is impossible. You have to let go of your old views if you want to change your life.