Mental models have inertia — things that users already know tend to stick in their mind, even when those models aren’t helpful in the current situation. This can cause problems for designers who aim to create a new way for users to interact with their product.

When you do something new, you have to overcome the inertia of users' existing mental models. Because of this, it’s best to only create something new when it’s superior to the old way of doing things. Take Netflix, for example. Users expected to have to complete an order before DVDs in their queue would be sent to them. But in reality, Netflix would automatically send the next DVD in a user’s queue when they returned their last DVD.

Users had to adjust their mental models to this new way of doing things, but considering Netflix’s success, they found it worth it to do so.^[1]