The repeated theme of unrequited love across a lot of creative media really expresses true things that relate to the psychological underpinnings of this concept. I think very few of us can rationalize wanting someone who does not love or want you back and I'll go more into this later but a love that is unrequited is very much tied to our brain chemistry, it's tied to reinforcement and behaviorist theories as well as attachment style as well. There are core aspects of the human psyche that inexplicably lend themselves to experiencing unrequite love even if it's from a distance.