When someone believes that they are absolutely 100% certain that something is / is not about to happen and then (often immediately) the complete opposite happens. This is known as a "Scarrottism".
People who often do this are said to have a bad case of "Scarrottosis".
In the car
"There's no way in hell she's going to get into that parking space!!! Oh, she's in..."On the phone
"If you think they're going to the answer the phone on a Sunday, you're insane!! Oh, hello..?"
Both of the above are examples of scarrottism.