Cognitive dissonance is defined as the uncomfortable feeling caused by holding two contradictory ideas simultaneously. I remember experiencing this phenomenon very vividly as a child in a simple example. I was playing with a ball. I dropped the ball and it rolled away. I thought it was behind a piece of furniture, but it happened that it rolled much further away. I looked behind the piece of furniture where the ball was supposed to be...and it wasn't there. When I saw it across the room, I almost refused to believe it. I became very upset. It was supposed to be here, and it was there.
This experience left a strong impression on me, and would translate later in life to other experiences. When meeting with friends, I expected to have a good time, but I would be unhappy instead, for example. Going to a dance, or a social event, I expected to be a certain way, and it turned out that my assumption of who I was and how I would act was totally off. How to explain this? Only that sometimes we prefer our ideas about reality to how things actually are.
Of course, this applies to faith. I imagine God to be this, and he is that. I expect my prayers to be answered, and they are not. The reality of God does not square with my concept of God. To be truthful, I think cognitive dissonance is a necessary stage in spiritual development that occurs when we attempt to live in full reality instead of our childish illusions of faith.
I have a feeling marriage is not going to be whatever it is I have imagined in my head. That is ok. As long as I let go of the ideas when the reality presents itself, I think we will be ok. It's when we try to hold on to the ideas in the face of reality that we start living unauthentically and experience that cognitive dissonance, that uncomfortable, troubling feeling that things are not what they seem to be. That is when rationalizing, and living in unreality begins. Living in unreality is never authentic, and so recognizing the phenomenon of cognitive dissonance can help us develop further into the person we are...not the person we are supposed to be.