system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why do we cry?

Why do we cry when we feel

* Physical pain
* Emotional (e.g. loneliness, loss of loved one etc.)
* When cutting onions (and why does chewing gum stop this? Does chewing gum stop us from crying during physical pain?)

EDIT: I was let down by the inconclusiveness of this thread, but appreciate the answers. I'm making it my life goal to find out why we cry.
gpt
No-one has a definite answer. We have a good understanding of what tears are made of and how they come out of the eyes, but not what the actual function is. Some say that it is to do with the release of certain chemicals which have been building up inside the body when we are stressed. Others think it evolved as a way of communicating to others that we need help or comfort. But neither of these explanations is completely satisfying so it is still being debated.

Onion tears, on the other hand, are a completely different matter. They happen because when you cut into an onion it releases chemicals that were inside the onion into the air (a bit like suddenly being able to smell an orange when you start taking the peel off). These include acids which are irritating (and also explain why raw onion has such a sharp taste). When they get into our eyes, the eyes respond with tears to flush out these irritating chemicals.