This chapter is an indispensable part of the framework for the design of digital behaviors, as it lays the foundation upon which user behavior when engaging with digital services can be anticipated. The core principle to grasp is that the probability of a user repeating the use of a digital or virtual service is primarily linked to two variables: satiation of the drive and the emotion generated. The satiation of the drive is elucidated by the drive reduction theory, whereas the proposal of how emotion or excitement selects behavior is explained by Frederick Sheffield’s induced emotion theory. The key point here is the attainment of the reinforcer, which is the element that induces changes both in the reduction of the drive and in the induction of emotion. In relation to this, it has also been suggested to differentiate among drive, motivation, and reinforcer. Drive is an internal state of physiological or psychological origin, acting as a vector of behavior, but it does not energize the behavior per se. This drive triggers a biochemical cascade within the organism that intensifies over time, and its non-satiation progressively energizes behavior, resulting in a subjective experience defined as an emotion, which initiates goal-directed behavior. Finally, a list of different types of drives (survival, sexual, social, and meta-cognitive) has also been offered, indicating the potential needs of users when turning to a digital or virtual service.