a will to live
A will to live is like having a tiny engine in your chest that goes 'I'm not giving up yet!' even when you're too tired to move.
I had a will to live when I finished my third slice of pizza and still tried to do my homework.
My dog has a will to live because he still barks at the mailman even though he's been dead for a year.
My brother has a will to live because he still texts me every day even though he knows I hate it.