I was talking with a lady at work recently, and somehow the subject of emotions came up. At one point she said, "It's probably just a girlie thing. You probably don't know what I'm talking about."
I told her that it was a "human thing", and that men frequently feel the same way - they just either hide it or try to control it. When I thought about it later, I found myself wondering why men do that.
I think it's out of necessity. I used to think it was cultural or societal conditioning - and I still think that's part of it - but there's also a pretty practical reason for it.
Consider the fact that for most of human history (and even today, to a large degree), most societies have been paternal in nature - the men have been in charge. With this in mind, all you have to do is look around - today, in history, whenever, it doesn't matter - and you see many, many instances where men have given free rein to their passions with disastrous results.
Occasionally an artist, or a builder, or someone else with constructive passions will demonstrate how great man's potential is, but more frequently you run across the destructive personalities who consider their personal passions to be more important than anything else - That's when you get Napoleon, Hitler, Alexander, Stalin, Mao - the list goes on almost endlessly.
So, I think it's a very good thing that men - the more aggressive of the genders - try to control their emotions. It may be that we are aware of our destructive and selfish desires and passions and choose to suppress them.
Either that, or we're just afraid of emotion. You decide.