The tendency for users to make habits out of common and repeated actions to the point where they no longer need to think consciously about doing them. For example, pressing ctrl-S to save something. This can be leveraged in design to improve efficiency and make a system easier to learn to use. However, it also means that the user might wrongly assume something will work a certain way in accordance with what they're used to doing. This is why it's important to verify the gestures in your design all do expected things.