What is a key factor that differentiates expert performers from good performers, according to K. Anders Ericsson?

A key factor that differentiates expert performers from good performers, as outlined by K. Anders Ericsson, is the amount of hours of deliberate practice they engage in. Ericsson's research emphasizes that consistent, focused practice—beyond simply spending time at a task—is what enables individuals to reach high levels of performance in their fields. This deliberate practice involves setting specific goals, obtaining feedback, and continually working on the aspects that need improvement.

Unlike merely accumulating hours, deliberate practice is characterized by its intention and structure, which is crucial in developing expertise. While interpersonal relationships, intelligence, and access to resources can play roles in performance, they do not represent the primary differentiator that Ericsson highlights in his studies on expertise. Focusing on purposeful practice is what drives significant improvement and achievement among expert performers.