BJFogg, founder of the Persuasive Technology Lab at Stanford University, with his Behavior Model explain what stops users from performing behaviors that designers seek.
Behavior Model BJ Fogg
if users are not performing a target behavior, such as rating hotels on a travel web site, the FBM helps designers see what psychological element is lacking. …
… The FBM highlights three principal elements, each of which has subcomponents. Specifically, the FBM outlines three Core Motivators (Motivation), six Simplicity Factors (Ability), and three type of Triggers. The subcomponents define the larger elements.
(source: behaviormodel.org – BJ Fogg)