I don't think it's physical conditioning ... it's mental and generational
not to bring outside issues in but the payers back then were raised by WW2, Korea, and Nam vets ... and several of the coaches fought those wars and or grew up in hard times
it was an era of "never let the other guy out work you"
Landry grew up in a dirt town in rural Texas during the depression, fought in WW2, and played in the NFL when there were no face masks and then in the NFL with no face mask flags - that's rough.
until you've lived through a mess you don't understand
"winning isn't everything - it's the only thing"
remember NFL Films "a violent game played by violent men"
the current commission would never allow such statements in an official broadcast - as not nice enough
these kid's just aren't as tough by nature - it's the times we live in
if these youngsters grew up and the electricity was off sometimes or they didn't get an iPhone pre-puberty they think they had it hard ...