The "aha moment" is also known as the eureka effect. Psychologists call this "insight problem solving", which is terrible for interviewing since like you said since it isn't a problem that you can build up towards solving. As a teacher, I try to make sure my assignments/quizzes don't fall victim of this.

For anyone interested, there are a lot of interesting studies on the topic if you search on Google Scholar. You've probably already seen matchstick arithmetic problems before (i.e., move a single matchstick to make the equation valid).