The emotional domain of many men tends to be relatively narrow. They are fearful of the consequences, culturally and personally, of expressing their emotions. No one wants to be held in contempt, humiliated, or ridiculed at the water cooler for behaviors deemed unmanly. The absence of a language to describe men's inner world compounds the issue even more. Men do not express themselves in the same vocabulary that women use.
Men tend to distrust their feelings.
Many fear that if they begin to let their feelings out, they might not be able to shut them off. This can be a terrifying and repugnant thought. While women sometimes worry about this, too, their level of anxiety is not nearly as acute. By viewing emotions as uncontrollable and volatile, men reinforce their belief that it's safer to keep feelings concealed. Because men are given little encouragement to express their emotions, they are hesitant to expose any emotional vulnerability.