misexpected 

To inadvertantly place trust in something turning out a certain way, but finding out later the trust was based on a false pretense. Different from unexpected because it was a total screw-up, not just a surprise.

The US Government misexpected that throwing a little debt at a lot of debt would lead to less debt.

misexpected by mycbrad July 12, 2009

Misexpectation 

To have the incorrect perception of what the outcome of a situation should be due to missing the main idea or key points defining the situation.

The overlord has serious misexpectations for the play, he thought it was a comedy beforehand when it was actually mystery.

Misexpectation by Vocabulomorph October 22, 2015