In bodybuilding terms, "cutting" is being under calorie deficit. It can wreak havoc with your mood systems and that's why people can't keep it up. Start small.
It's not just moods, it's also hunger. AFAIK, fMRI studies have shown that in morbidly obese people, the hunger part of their brain is constantly activated. They're actually hungry all the time, they have an irresistible urge to eat. I'm sure the large majority of them wish they were thinner, but to them, it's a painful struggle against biological urges. I used to be overweight, lost weight, but it's a constant strug…
I've pretty much learned to accept it's something I'll have to deal with for the rest of my life, rather than "I was fat once, I got rid of it, it's no longer a concern, the end."
It totally pisses me off to see people who can't manage to do the same being judged in awful ways by people who were lucky enough not to have to do it in the first place or for whom it was apparently relatively easy and assume it'll be just as easy for everyone else.
I count myself amongst the lucky, I'll never say "I could do it, so you can too." It's counter productive and an awful thing to hear when you're already really trying.