Zeigarnik effect is a psychological principle stating that people remember and feel compelled to complete unfinished or interrupted tasks better than completed ones. In UX design, this effect is leveraged to enhance engagement by creating a sense of progress and encouraging task completion. This can be achieved through progress indicators, checklists, gamification, unread notifications, and onboarding sequences. By providing clear signifiers of additional content and artificial progress cues, designers can motivate users to return, explore, and complete tasks, ultimately improving user retention and experience.