A neutral stimulus repeatedly paired with a significant one comes to elicit the response by itself.
Pavlov's dogs salivated at the bell by 1897. The general point is that the pairing need not be noticed: advertising, phone notifications and the sound of a fridge opening all work this way.
In practice
- A team that gets bad news in the same recurring meeting comes to dread the calendar invitation.
- A phone notification tone paired with work messages produces the work feeling on a Saturday, and nobody chose the pairing.