Students often mistake familiarity with true mastery, creating a dangerous "illusion of competence" where recognizing information feels like genuine knowledge, but they struggle when asked to recall or apply it independently. This cognitive bias, strengthened by passive study methods, leads learners to overestimate their understanding. Teaching materials (even informally or imaginatively) actively counters this illusion by requiring deep processing, active recall, structured organization, and revealing gaps in knowledge. It introduces powerful methods like teaching imaginary students, peer-teaching in study groups, employing the Feynman Technique, and writing explanations for others. Ultimately, adopting the teacher mindset transforms surface familiarity into real mastery, exposing and filling gaps in knowledge and ensuring solid, reliable understanding.