Growing up boys are pushed to try their hardest and to be masculine. Many of them are encouraged/expected to play sports, sometimes even if thats not what they want to do.
As they grow up they are taught to toughen up. They put on this tough guy exterior. So that means no crying, or in general showing any sensitivity.
In today's society when boys become adults they are expected to get a "Masculine" career, like a lawyer, doctor, construction. When they have a family they are supposed to go to work and bring home the bacon.