The Aha! Effect refers to the common human experience of suddenly understanding a previously incomprehensible problem or concept. Some research describes the Aha! Effect (also known as Insight) as a memory advantage, but there is conflicting results as to where exactly it occurs in the brain, and it is difficult to predict under what circumstances one can predict an Aha! moment. Another way of expressing this is "the Eureka" moment.

The expression "a-ha" is made when someone makes a discovery. "A-ha, I have found my shoes!" "A-ha, my invention works!" "A-ha, that's why women do those things!" :-) I think there was a book by that name, but my memory of the "a-ha effect" is understanding without a long time of thinking. Kind of like satori if you know that Buddhist word. New information triggers new understanding suddenly, is what I believe they are saying.