We get this word from the character of Cassandra in Ancient Greek stories. Cassandra was "blessed" with the gift of prophecy; that is, she knew what was going to happen. Nobody would listen to her, of course, rendering her powerless to alter the nasty future she saw, and as a result of this she went a little schizy. This type of I-know-what's-going-to-happen-but-I-can't-stop-it conflict has since been named the Cassandra Complex.

I've come to realize that almost all children of average intelligence or better experience this complex.