Chris Pratt before and after.
People say the hardest thing about "going on a diet" is feeling deprived of all their favorite foods. They intentionally fail to connect the uncontrolled eating of their favorite foods to the inevitable result of that: obesity.
The psychology of it all is complicated.
It comes down to choosing your brand of deprivation. "Depriving" one's body of the foods that made one fat in the first place in favor of a better looking, better feeling, better functioning body sure doesn't sound like deprivation — it sounds more like a well-deserved reward.
Weighing the momentary pleasure or comfort of eating whatever one wants whenever one wants it in any amount one craves, against feeling, looking and functioning better 24/7 is no contest. This is why people concoct the most complicated and convoluted justifications for the poor physical state they are in, because the solution is so obviously simple: eat less, move more.
I like snack foods almost as much as the next guy, but being in shape, knowing I can run or climb from danger, looking good, feeling great physically rather than feeling diminished and old rather than worrying about the outcome of my poor condition, FAR outweighs any temporary minute-long satisfaction I get from gorging on pizza or ice cream.
I do eat pizza and ice cream, but the frequency and amount I can enjoy without it taking a physical toll are well known to me, because I pay attention. Often I read that seeing one's self in a photo or video in their obese state is what snapped people out of their obesity denial. It's intriguing that someone can be carrying around 50 extra pounds or more night and day and psychologically speaking not be aware of what a constant burden that is, yet one view of themselves as others view them can change their entire outlook.