What would cause someone to become a stalker?

Question

What would cause someone to become a stalker?

Answer 1

1. The inability to accept that a relationship is over;  2.  An unhealthy obsession with an individual, in which the stalker believes they have, or could have, a "relationship";  3.  The objectification of an individual for personal gratification

Answer 2

Yeah, whatever Compassionate Princess said including boredom.

Answer 3

Well, I'd put mental illness pretty high on the list.  There's often a delusional aspect to it.

Also, being rejected by someone they don't feel they deserve to be rejected by.

And probably a lack of socially supportive relationships in their personal life - a lack of good friends, and difficult relationships with parents and siblings.

Basically, it's a highly intrusive kind of behaviour, very damaging to the person being stalked, and needs to be dealt with swiftly and thoroughly.