This is a neat series, and I think "the lies we tell ourselves" represents one of the most important contributions of psychology. Have you read the work of confabulation in split brain patients?

Some patients have the tracts in between their two hemispheres severed (sometimes to prevent seizures), so the hemispheres no longer communicate well with each other. You can send visual information to particular sides of the brain, since the visual field is lateralized. Here is the classic experimental example: the right brain sees a snowy scene, while the left-brain sees a chicken leg. The patient is asked to choose between a few pictures that best relates to the scene that they saw.

One of choices relates to the snowy scene (a shovel) and one of the choices relates to the chicken leg (a chicken). If you now ask the patient to point to their choice, each hand points to a different symbol. The right hand (controlled by the left side of the brain) points to a chicken, and the left hand (controlled by the right side of the brain) points to a shovel. Now the cool part (that relates to cognitive dissonance). Language is also usually lateralized to the left side of the brain. If you ask the patient why he pointed to a shovel, the patient quickly makes up a story to explain their behavior (e.g. "well, you need a shovel to clean the chicken coup") even though that hemisphere had nothing to do with the behavior.

We're probably doing this rationalization all the time, but it takes an extreme example like this to make it so obvious!