Imagine that you’ve never seen an iPad, but I’ve just handed one to you and told you that you can read books on it. Before you turn on the iPad, before you use it, you have a model in your head of what reading a book on the iPad will be like. You have assumptions about what the book will look like on the screen, what things you will be able to do, and how you will do them—things like turning a page, or using a bookmark. You have a “mental model” of reading a book on the iPad, even if you’ve never done it before.
If you’ve used an iPad before, your mental model of reading a book on an iPad will be different than that of someone who has never used one, or doesn’t even know what iPads are. If you’ve been using a Kindle for the past year, then your mental model will be different from someone who has never read a book electronically. And once you get the iPad and read a couple of books on it, whichever mental model you had in your head before will start to change and adjust to reflect your experience.