The problem with that is, "realistic" for a lot of people is well below their potential and colored highly by their own laziness and self doubt. Constantly setting "realistic" goals will have people in a pretty stagnant place and the "success" they feel will be barely earned. Which then leads into the spiral of "well I didn't eat 15 cakes today, only 13 so my diet was a success" type mindsets, because they've taught themselves (and their brain's dopamine) to trigger on minimal effort places instead of being reserved for motivating to big ones.

Its not that genetics can be ignored. Its that people are still people and filled with all the failings and neuroses that brings, leaving them with an easy excuse and the ability to feel good about lowered goals will have 9/10 people just flounder around worthlessly like that. Whereas "impossible reaching" goals might be delusional and capable of some pretty big letdowns, but its also capable of bringing them well beyond where they thought they'd ever get too.