>But life is not fair and it's not going to happen always.

The world would be a much much much much much much shittier place if everyone accepted things and never pushed back.

>Not being able to accept that shows immaturity.

I find not being able to accept that other's have a different but equally valid approach to life shows immaturity.

Why can’t we try and change things we feel are unfair? Sure, we can’t change everything and we don’t always get what we want, but surely we can try, like asking someone to improve their behavior?

Either you're high status enough to not care about these things, or you get walked all over. For most people fighting for recognition on important or valuable things is worthwhile.