You asked me why do men lie.  

The question took me by surprise.  
It's very deep and philosophical but 
I'm sure you don't want a long answer.  
So, I'll try to keep it short.
 
There are so many possibilities in my response, 
but I think it is mostly an attempt to protect 
the friend or friendship.  Really, couldn't
you have been a little more specific?  
It's just too broad a question, too general.  
If you could have given me a specific case, 
I could better hypothesize a response.
 
Some men are driven by hunger for power, 
others for acceptance and still others 
for the illusion of love and romance 
simply to feed their drive for sexual 
fulfillment and pleasure.  But then, 
don't women have these same drives?
 
From a Theological perspective, it is the 
"sin" nature of all mankind (men and women) 
to lie.   The closer we come to our creator 
in a spiritual relationship, the less likely
we are to lie (or conduct other matters of 
the heart that can vex the soul like cheating
or stealing).  This could also be considered
achieving your "karma" as well.  My personal 
belief though based on sociological "present 
day" society studies is that there is greater 
turmoil and considerable loss in fundamental 
self-respect and self-esteem resulting in a 
greater breakdown in society as a whole.
 
People are also very "Class" aware of
themselves, and despite what you and I may 
think, there is a class order in the US as 
well as in other countries that would influence 
people to lie.  Take for example that country 
girl who's BF was from Georgia.  I have no 
doubt that she lied about her relationship.  
She had so many financial problems too.  
She was thrown out of her apartment or home 
(or they were trying to remove her).  
I really think it was a status "thing".  
She wanted "acceptance".  I suspect that 
her lies caught up with her and she 
disappeared out of sight for a while 
and subsequently reappeared in another 
relationship and was talking of marriage 
again very quickly but with another man.  
I'm amazed at situations like that.  
She has a basic necessity needing to be 
filled and went to great lengths to 
achieve her goals, and did so at the 
expense of lies to everyone including 
herself.
 
So we have a fundamental breakdown 
across society as a whole from all 
walks of life, starting with the 
leaders in society.
 
Look at the President of the United 
States, A position of tremendous power 
across the entire free world, and even 
Slick Willy lied.  And the world sits 
back and laughs!!!!!!  I ask you, who 
is left to look up to and admire?
 
Why do men lie???  I really don't know.