The Goldilocks Effect: Why Has The Boeing 787-9 Sold So Well?

In marketing, there is a technique called the Goldilocks Effect. It’s based around something not being extreme in one direction or the other, rather landing in the comfortable middle and therefore having appeal. But how does this principle apply in aviation? A good example is the Boeing 787-9, and how it has sold so much better than the 787-8 and 787-10.