We desire collecting all pieces of a set more the closer it is to being complete
The Persuasive Patterns Card Deck is a collection of 60 design patterns driven by psychology, presented in a manner easily referenced and used as a brainstorming tool.Get your deck!
Completing a set of logically grouped tasks or items allows for achievable goals and small successes. Consider how you can have multiple levels of sets and what kind of things or information suggests logically grouped sets and set completion. This principle also applies to other things left incomplete such as puzzles, pictures, or sentences.