Scratch is widely used as an introductory educational tool for computer programming. However, little is known about how the action of adding favorite projects on Scratch social media influences programming skill improvement. On Scratch social media, learners select personally intriguing projects to view and learn from. Favorite projects both motivate users to participate on social media and serve as scaffolding material for learners. In this study, we analyzed a dataset of 50,786 users from 5 years of longitudinal activities on Scratch social media using the Zones of Proximal Flow theory. To understand how favorite projects influence learners, we compared the frequency of social media use and programming skill improvement between users who did and did not add favorite projects, and we found a significant difference in programming skill improvement. Among users with favorite projects, there is a proximal difference of two to five Dr. Scratch scores of the favorite project above users' capability level, which maximizes the frequency of social media use and programming skill improvement.