I think it came from someone who was gardening who figured out that 80% of his crop came from only 20% of the seeds he planted.
The idea is that 80% of results will come from 20% of your concentrated effort.
Eg: if you run a business, you could have 10 clients. But if you really look at the numbers you could notice that 80% of your profit comes from only 2-3 clients.
Instead of wasting time on the other 7-8 ones, it is better to find more clients like those 2-3 (this example is used in the book the 4-Hour Work Week)
I do not know what you mean about women, but 80% of the good stuff will come out of only 20% of your effort - which is also why doing too much turns women off.