True, it's a John Wayne film (4)
I believe the answer is:
grit
But I can't explain it at all! Could you help me understand?
(Other definitions for grit that I've seen before include "Courage - clench - small particle of stone" , "Coarse sandstone - strength of character" , "Guts and gumption" , "Determination - which is found on winter roads" , "Gravel or colloquial courage" .)