>People had/have a hard time accepting "eat less to not be fat".

It's kind of like saying "Smoke less to avoid lung cancer". You can say eating is a fatal addiction. If you stop you die. The hard part is is balancing it so you keep on living and avoid the negative health outcomes.

Why is this hard? First the cause and effect are separated by a lot of time. If I eat a sweet fat sugary treat I get the good feeling RIGHT NOW. The negative health effects are way later.

Other reasons it's hard is our eating habits are mostly created in our childhood and very hard to break as an adult. If your parents fed you poorly you're at a significant health disadvantage.

The last one I'll list is crap food marketing. The most unhealthy crap seems to have the brightest packages to catch our eye. It has huge amounts of salt, fat, and sugar, things our evolutionary body craves because the number one thing it wants to avoid is starvation.

So yea, it is reachable, but it is not trivial at all.