In my opinion, mental toughness is learning to do those things that are difficult for the individual. My son was very afraid of heights at the beginning of the season. He had to be led on trails I was indifferent to. After few times out, he'd have to stop to gather the courage to go across a particular section. Sometimes he'd stop for 5 or 10 minutes before going, but he always did it.

For myself, what others might perceive as toughness is simply indifference to the things I can't change. I'm not one to go past my personal boundaries of endurance, but the more I get close to them, the bigger they get.
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