I believe falling in love, is a breed of pain.
You see, we learn to fall in love with people. Slowly depending on the other for emotion, affection, and joy. But once separated... We have accustomed our terms from "falling in" into "falling out". Yet in reality, the heartbreak we experience is just another form. The lust for affection in a positive response is only changed into the affection in a negative response.
Which would only explain as to how people are scared to fall in. Sooner or later, you will fall out.