Take the old adage “treat others how you would want to be treated” - is that something you believe because you’ve just been told that for so long? Or is that something you intrinsically believe in regardless of what others have said?

For what it's worth, this is essentially the "tit-for-tat" strategy from game theory, and you can rigorously prove it to be a superior cooperative strategy in many situations. Essentially, cooperation with others enables greater community success than everyone going alone, but trusting others always exposes you to selfish people that will take advantage of you. The optimal strategy is to cooperate by default, but if someone reveals themselves to be untrustworthy, stop cooperating and ideally work with others to punish them.

You actually see this bear out in nature in other animals as well. Vampire bats will share blood with other vampire bats that didn't successfully feed, but they also keep track of individual contributions, and if they identify that a bat is freeloading, they'll stop feeding it. By default, they cooperate to help each other, but if a selfish actor is identified, they stop helping it.

In the abstract, so long as most actors aren't selfish and the cost of being betrayed isn't too high, tit-for-tat is the optimal strategy.