On suicide.

What is it with suicide?
I'm not trying to be judgmental here. I'm just morbidly curious. How does their mind work, these people attempting suicide?
I've seen this up close. My grandfather basically spent his entire life trying to die. He suffered from chronic depression, and I remember him as either really high up or really, um, resigned? He was about sixty when he was 'finally' successful at his attempt. And then that was it: the minute he realized that he had made it happen, he wanted to undo it all back. He wanted to go back home.And he wanted to stay.
It was too late by then, whatever poison he had swallowed was shutting off his organs like candles in the rain. But the point is, I've never seen him fight to live as much as he did when he realized he way dying. Maybe he realized he was scared of dying too.
I don't know how it works with other people, but I hear this is very much the case with pretty much anyone who attempts suicide.
One of my mother's friend's husband hung himself in the garage. They later found scratch marks all over the wall, what I assume to be his last attempt to stay.
So I ask, how? Why? Why? Are these people so horribly depressed that they think there is nothing worth staying for anymore? Are they so scared to live that they choose to die instead? Because, paradoxically, that's quite a brave move, deciding to end it here and move forward when nobody really knows what's there to move forward to. If there is anything at all.
Or is it that they've gone so numb that they try to feel alive the only way the know how? Giving themselves the highest thrill?
Or maybe, is it that they need a reminder of their own mortality to help appreciate their life more?
Maybe it's just as simple as not knowing what to do with themselves?
This was all brought up by a friend absently saying she feels like killing herself sometimes. I know she didn't mean it literally, but I don't think the general public understands the severity of such a statement.
How can anyone be afraid to live yet not be afraid to die?