Friendship is a strange idea, difficult to quantify and, at times, even more difficult to maintain. Clearly a friend is someone you enjoy spending time with. However, a friend is also someone you continue to support even during periods when they are considerably less pleasurable to be around. The loyalty of friendship often contains a kind of tautology or feedback loop: the longer you are friends the more loyal you become, and the more loyal you become the longer you remain friends.
Jacob Wren, Rich and Poor
friendship, transactional-relationship