I agree with Donna that loyalty is a personality trait.

I think you're more likely to express the trait if you've been conditioned to because of events in your past, like Donna was, but sometimes people become really loyal because of how they grew up and evolved as people in general.

But sometimes people grow up in very dysfunctional, and sometimes abusive, families where there are no close connections, and loyalty to friends becomes extremely important.

I've been loyal to a fault in the past. I've (mostly) learned it's at least more important to protect myself over others now, and not get involved in contentious situations...