You just gave a brilliant presentation. Your boss commended you. Your colleagues are impressed. A neurotypical person would internalize this as proof of their competence. You, however, go back to your desk with a racing heart, thinking, "I barely pulled that together last night at 3 AM. If they knew how disorganized I actually am behind the scenes, they would fire me immediately."
This is ADHD Imposter Syndrome. It is practically universal among high-functioning adults with the disorder. You don't suffer from low self-esteem; you suffer from a lack of reliable self-trust. You know that you are intelligent, but you also know that your intelligence is conditionally locked behind a wall of executive dysfunction. You cannot predict when your brain will cooperate and when it will crash. Because your performance is erratic, you attribute your victories to external factors: adrenaline, last-minute panic, or sheer luck.
Furthermore, the ADHD brain struggles to encode positive long-term memories due to a dopamine deficit, but it hyper-encodes failure and criticism due to Rejection Sensitive Dysphoria (RSD). Your brain maintains a meticulously detailed, easily accessible filing cabinet of every mistake you've made since the third grade, while your successes are immediately discarded as 'flukes.'
You cannot logic your way out of Imposter Syndrome, because your fear is based on the entirely accurate observation that your methodology (panic-driven hyperfocus) is inherently unstable. The solution is not to "believe in yourself more"; the solution is to externalize your proof of competence and systematically decouple your worth from your chaotic process.