What is the one thing about Woman, that a man can never truly understand?

IMO it's that men underestimate women's intelligence. Why do they think we don't know the ins & outs of football, cricket, car racing, or how the family car works or what makes the dishwasher go? Just because they can't grasp the intricacies of how to operate the vacuum or the sewing machine, they think we are equally dumb!

Maybe this isn't exactly what you were after in the way of an answer, but it's what I think.

the extent of pain a woman get while giving birth to a child

Mode swings

the fact that women are not inferior to you in any way but strength and you fail to understand that they are not your possession but an individual in their own right

giving birth to his kids and carrying them for 9 months in the womb

:)

i could give you a whole list..but i'll stick with two.

1) why we feel the need to look our best for our partners.

2) labour pain...not that i've felt it, but i can only guess its excruciating - and a man will NEVER feel it.

=]

Her innocence. There are somethings which woman knows but she shows as if she never knew. She ain't that innocent.

feelings

our tolerance