Comes in one of two forms:
1) Syndrome: A one time screw-up that is so foreseeable, that you have no idea how you made the mistake.
2) Disease: A lifetime of ridiculously terrible screw-ups that have complete an utter alternatives, yet someone makes that mistake and can't see where they went wrong. Cases can range from bad to severe based on the symptoms.
1) "Dude, I can't believe I walked into that lamp post. I must have Derple Dyslexia Syndrome.
2) "Man, that driver has ran 3 red lights in a row and just pulled out in front of an 18-wheeler. He must have Derple Dyslexia Disease.