Metacognition, the ability to monitor and evaluate your own cognitive processes, was formalized by Flavell (1979) as a distinct domain of cognitive development. It includes self-monitoring ("how am I doing?"), self-evaluation ("was my estimate accurate?"), and self-regulation ("what should I adjust next time?").
Barkley, Murphy, and Fischer (2008) documented that ADHD adults significantly overestimate their own performance and underestimate task duration. This isn't optimism. It's a measurable metacognitive deficit: the internal feedback system that tells you "this is taking longer than you thought" doesn't fire accurately.
Toplak, West, and Stanovich (2013) showed that self-report measures of executive function and performance-based measures diverge significantly in ADHD, confirming poor metacognitive calibration. ADHD individuals think they're performing better than they are, and think tasks took less time than they did.