An excerpt from The Tipping Point by Malcolm Gladwell, quoting psychologist W. Mischel on human behaviour and perception:

When we observe a woman who seems hostile and fiercely independent some of the time but passive, dependent and feminine on other occasions, our reducting valve usually makes us choose between the two syndromes. We decide that one pattern is in the service of the other, or that both are in the service of a third motive. She must be a really castrating lady with a facade of passivity - or perhaps she is a warm, passive-dependent woman with a surface defense of aggressiveness. But perhaps nature is bigger than our concepts and it is possible for the lady to be a hostile, fiercely independent, passive, dependent, feminine, aggressive, warm, castrating person all-in-one. Of course which of these she is at any particular moment would not be random or capricious - it would depend on who she is with, when, how, and much, much more. But each of these aspects of her self may be a quite genuine and real aspect of her total being.

I love this passage.

(update: My girlfriend pointed out that this is true for guys as well, except maybe the castrating part... I know of no equivalent action against women...)