I always take my girls to the movies, and because they are young, we always watch animation. No matter which animation movie we watch, I always enjoy them, especially Pixar/Disney movies.
Great Pixar/Disney movies operate at two levels.
The story, characters, and visuals works for the kids. The humour in the dialogues works for the parents.
They need to do the job on both levels because young kids need their parents around to watch these movies and enthusiastically accompany them to the amusement parks.
Great products work the same way.
Great products are simple enough for the newbie user but have layers of complexity that get the job done for the more advanced user.
It is easy for a product to work on one of the two levels. But, the challenge is to work on both levels while preserving the simplicity.
It is why building simple products is anything but simple.