"A friend in need is a friend indeed. "
Friends are normally made by a common interest. We go to school together, we work together. In this day and age, we are more likely to make friends outside of these interests, e.g. our hobbies, the gym, cooking classes. More than not, we probably won't have that much in common except for how we meet but...opposites attract right?
Are friendships better made when you don't have that something in common? When it is an act of selflessness or altruism? Wouldn't you feel very grateful that someone disadvantages themselves to help you out? Would you not feel compelled to better of those people, even if it is trivial like lending you a food processor when your blender is broken?
"A friend is someone you can use over and over and over and over and over..."
- Ancient coffee mug quote