Why do people complain?

People come & go quite recently.
They tell me they are sad,
They tell me they are lonely.

"I hate myself." Is the common phrase these people make.
I sit, I listen, I understand, an important part too someones troubles, for understanding is key.

But why do they complain?
When I try to help, when I give advice, advice that came from my brusied and burnt out heart, ran dry from all these people that say the same, but mean not.

I'm not a therapist.
I'm not a doctor.
So why do you complain?