Seneca opens Letter 3 with a distinction that reframes every significant relationship you have.
There is a difference between calling someone a friend and actually treating them as one. A friend in Seneca’s frame is someone whose development you are responsible for and who holds the same responsibility toward you. An acquaintance is everyone else.
Most people have large networks of acquaintances they call friends and almost no genuine friends. This is not cynicism — it is an accurate diagnosis of what happens when the word friend is applied to anyone you know and like, without the trust, honesty, and mutual accountability that genuine friendship requires.