What makes us cry?

Why do we cry? I dont mean stress or loss or whatever, I mean WHY do we cry? It's always been on my mind, and I just wondered

when a boy sayz no to me

Crying is a natural emotion that we can't help doing.
We cry for allot of reasons. It could be sadness, stress, happiness, joy, spiritual reasons, frustration, anger, or just normality.
We're all human and we need to cry to get it all out. Otherwise if we didn't cry, we'd probably get sick and would probably need to go to the doctors or for that matter the hospital.
Crying is something that we as animals, and humans can't avoid.