self-interest can strengthen bonds
Even in friendships, appealing to self-interest can strengthen bonds. Suppose a person needs help moving to a new house but feels awkward asking their friend for a favor. Instead of framing it as a one-sided request, they could point out how helping each other has always been part of their friendship.
For example, they might say, “Remember when you needed help with your project last year, and I came over? Well, I could really use some of your muscle to help with my move!” By reminding their friend of the reciprocity that already exists in their relationship, they appeal to the friend’s sense of fairness and mutual benefit.
The friend may feel inclined to help, not just out of duty but because they see how it’s part of a mutually supportive relationship.