The most influential source of efficacy judgments is performance attainment.

Performance attainment, or one's personal experience of success or failure in a task, is considered the most influential factor in shaping an individual's beliefs about their own efficacy or ability to perform that task. Other sources of efficacy judgments may include vicarious experiences (observing others' successes or failures), verbal persuasion (encouragement or discouragement from others), and physiological or emotional states (such as anxiety or stress). However, research suggests that performance attainment has the strongest impact on shaping one's beliefs about their own abilities.