The Cassandra Effect (or syndrome or metaphor) has its roots in Greek mythology. Cassandra was the daughter of the king of Troy, and the god Apollo bestowed on her the ability of prophecy. However, she angered the god, and he turned her gift into a curse – she could see the future, but no one would believe her. When she later tried to warn the Trojans not to take on the mysterious giant horse left at their gates, they didn’t listen, which of course had disastrous consequences.
So today, Cassandra’s myth is invoked whenever someone made a prediction that turned out to be correct, but nobody believed it. It is also sometimes used in psychology to describe the feelings of people whose accounts of stressful events are not believed.