For me, the situation is what you can handle without complaint.
One of my friends is in cancer treatment. She just goes through it. No moaning about her fate. No "pity me" language. No neediness.
She goes and gets her treatments. She efficiently asks for the help that she needs. She's not ashamed to admit she's in pain, to cry in pain, etc. But, she does this *without* complaining all "woe is me!" and "no one understands!" and all that drama. she's just getting on with it with grace and grit.
So, really, grit is the ability to take on what is in front of you without drama. You look at the situation in hand and get on with what needs to be gettin' on with.
I find that when a lot of people face any level of hardship in their lives -- even the most modest -- they whine, bitch, and moan about it ad infinitum, seeking all kinds of assurance and "help" and what not.
I find that incredibly frustrating and annoying.
Shit happens. You accept and adapt. And eventually, you'll find a comfortable spot and have your rest. Or make due with whatever is comfortable enough.