Depicting characters of the opposite sex

I was taught to never write from the opposite sex's point of view. Being stubborn, I took this as a challenge and wrote a story from a female point of view, and failed miserably, according to the one female I asked (my wife).

I often think with the billions of people in the world, it's impossible to make generalizations about people male or female.  The kind of female I depicted might indeed exist out there in the world.

Here is something I just posted on facebook:
I tell my female creative writing students, when they dip inside the heads of men in their short stories using the omniscient narrator, that they make their male characters more thoughtful than men are. I asked a woman student my age what she thought. Her reply: there are a small fraction thoughtful men out there, well trained by their mothers.