Part of a man's strength is his ability to be emotionally stoic. This issue is often mistaken for the completely emotionless man that could not relax throughout much of the early to mid 20th century. There is a balance between being emotionless and too emotional - and this balance varies from man to man. In the end, each man finds his own emotional threshold, but one that allows him to not be overly emotionally reactive.
In the course of traversing the dominance hierarchy and being the leader he must be, men must make smart, unemotional decisions. If a man cannot control himself when faced with a 2 out of 10 problem, how does a man react and make cool, rational decisions when faced with a 9 out of 10 problem? The steadfastness that men call upon when making decisions is part of the iron backbone.
Men are rocks in the storm. When the world collapses around a man and his family (job loss, financial disaster, health problems with a child, and more), a man provides the backstop for his family. He is there to emotionally say "the world is collapsing around us, but I will guide us through this disaster." This unflappability is crucial not only for the dealing with the pain of disaster, but also in the face of pain when pushing toward goals. A grounded, complete man does hard things. To do hard things, he must be emotionally strong.
