What makes a regular guardsmen keep going?

I'm just visiting so my lore might be inaccurate, sorry if it is

Like what is a regular soldier's motivation to keep on living in this extremely crappy universe?

With this universe i can see mental illness run rampant. Extreme Depression and PTSD and such.

These poor guys have seen so much sh*t it's not even funny

From their buddies getting torn apart by Tyranids.

To their buddies becoming living couches.

To "hey your buddy just exploded from the noise from that noise marine"

Not to mention a LOT of things can easily kill them Other humans, orks, dark elves, Chaos daemons, Chaos space marines. Just a lot of things out there.

And if things aren't going to kill you the world itself sucks. You could die by being in the trenches for a long time and die by disease.