Why are men afraid to cry/show emotions?

I'm not sure if this is a good or bad thing to say on a predominantly male subreddit, but I'll say it anyway. I am a guy. I over hear my parents talking (my dad is a Vietnam vet) about how us guys shouldn't cry and that it's a sign of weakness. I feel like my parents take this attitude towards male emotions because my dad is a vet. My family is very traditional and my dad is very stubborn. My mom is also stubborn, but she is no where near as stubborn as him. How do I get my Dad to understand that me expressing my emotions, whether crying or just talking about how I feel, is just a normal part of human nature and is not a bad thing. I am not crying all the time. It's just when I am either upset or overwhelmed that I will express my emotions in that way.<br><br>&#x200B;<br><br>**TL;DR:** How do I get my stubborn dad to understand that me expressing my emotions and crying is just a normal part of being human?