How one-sided affection can become mutual affection

Nearly 30 years ago, when I still had no personal experience in relationships, someone told me that the most important thing which made them love another person was for that person to love them back. At the time, I had somewhat mixed reactions to this idea. On the surface, it sounded a bit sweet and romantic: You love me, and I'll love you back. That sounded kind of cute, but I had some issues…