The Octalysis Framework is a gamification design framework developed by Yu-Kai Chou. It lays out an octagon shape with 8 Core Drives for humans motivation:
1) Epic Meaning & Calling
2) Development & Accomplishment
3) Empowerment of Creativity & Feedback
4) Ownership & Possession
5) Social Influence & Relatedness
6) Scarcity & Impatience
7) Unpredictability & Curiosity
8) Loss & Avoidance
Games are fun because they appeal to certain core drives in humans that motivate us to engage in certain activities and increase engagement. Here, different types of game techniques can drive the user differently: some in an inspirational way, others in a manipulative and compulsive way. Everything that humans do is based on one or more of the 8 core drives.
Source: Yu-Kai Chou