Life before the marriage

Why is it often that the boy is like before the marriage but when he goes to see a life partner, why does he see himself very much?
Why does he look like he is a very good boy?
Regardless of how much it has been in relation to girls, but why does it look that they do not see the girls taking their eyes?
I think, not everyone is before marriage but it is necessary for all the know-wife to be aware of everything.