Job 3

Job 3:13

"For now I would have lain down and been quiet;
I would have slept then, I would have been at rest,

Job was asking why he couldn't have died before being born.  He's gone on at some length about how he wishes he had never been born, or died in the womb, or never even been conceived.  But for half the chapter, he just moans, and never explains why.  Obviously he's in pain from all his losses, and he wishes he could have avoided them.  But why not simply wish for death now?

Here he explains why.  If he had died as an unborn baby, he would never have known pain at all.  His life has, until recently, been very good.  However, it wasn't perfect, and there had doubtless been things to hurt him before this.  But if he had died before knowing the world, he would have always been at peace.  No joys, but no sorrows either.  At the moment, he sees that as an acceptable trade-off.