The gentleman I refer to in my signature had another saying "Your mind is your most important weapon."
I think there are several levels of toughness, all of which may be required. One level - perhaps the most difficult - is to continue living and functioning in a harsh and maybe hopeless environment. Examples would be the Bataan death march during WWII, or various concentration camps. It's one thing to endure life without cars and so forth - but it would be a challenge to believe that life is worth living on a slow-starvation diet, coupled with a harsh environment and unending work, and with no hope of a positive change. The temptation to end it all might be great.
Another level is to function in a harsh environment where plenty of hope still exists. The willingness to walk that extra mile (or ten, or hundred), continue to function without sleep, or whatever is required to accomplish short term survival. Going ten miles on a broken ankle, in a hostile area, and in a short period of time might be an example - there was a fellow I knew who did that. Of course, he had an ample supply of popcorn.
The third level is the ability and willingness to be ruthless in surviving. This could range from unsportsmanlike hunting to cold-blooded murder. It might well involve stealing the bread from another person's mouth. Or, it could simply require withholding aid to those who desperately need it.
Peak Oil will probably require elements of all three. Whether any of us have it is debatable; it's common to claim toughness, but such attributes are not at all common in the real world. I suppose the forge of circumstances will reveal the truth.