The global COVID-19 pandemic has disrupted traditional learning methods, leading to a surge in online learning. It has been found that the low course completion and performance are associated with online learning. There has been increasing and urgent necessity to identify effective and decisive ways to address these challenges. Self-directed learning and online learning attitudes are key factors that influence learning behavior and outcomes, while the general traditional statistical method often does not perform well in identifying those categories. To fill the gap, this study applies the fuzzy Delphi method and the fuzzy decision-making trial and evaluation laboratory (DEMATEL) method to clarify and analyze the relationship of influence among indicators of self-directed learning and online learning attitudes, develop a cause–effect model, and ultimately identify an effective and decisive strategy for improving online learning. According to the cause–effect relationship among indictors, the computer/smartphone and internet confidence, computer/smartphone usage, and computer/smartphone preference are the three decisive strategical ways for online learning. To improve learners’ attitudes towards online learning, teachers need to develop or improve students’ computer/smartphone and internet confidence, computer/smartphone usage skills, and develop their self-directed learning abilities to inspire and increase their willingness and ability to participate effectively in online courses. Moreover, this study first applies the fuzzy DEMATEL method to assess, analyze and develop a causal model of self-directed learning and online learning attitudes for academics to further explore and confirm the complex interrelationships among the key learning behaviors of online learners.