You don't!, forcing it, when the student isn't ready or doesn't care, is the source of students becoming numb to subjects and in some cases hate it for the rest of their lives without ever understanding them

If you don't need to teach non-interested students the material, then the job becomes a thousand times easier.

Exactly!. Is there any evidence that forcing content increases long-term life success to students?, Or is there at least some study on-going?

Schools have many impact vectors, forcing content learning is just one of them, and not necessarily a good one, I'm biased into thinking it's actually bad but it's overcompensated by its side-effects: place of gathering, exposure to higher-than-average smart people (teachers), introductions to some branch of knowledge, etc, and of course, forced-content consuming from interested students that probably would get better results from a self-paced learning system like Khan-Academy