Someone who is not born with all the electrical circuits connected flush. This is not a guy who you want to walk up to and ask too tough a question, especially if he is already working on a task such as breathing, walking, sneezing, or gazing. These people basically have nothing to write down if you were to hand them a resume. A general lack of complexity
Guy #1: Hey Jason do you think you could help...(interrupted)
Guy #2: Dude didn't you know?
Guy #1: What man?
Guy #2: Jason is what we like to call a single task completer, and he is already deeply engrossed in a four piece puzzle
Guy #1: Oh right bro, thanks. See ya Jason
Jason: (no response...because of the aforementioned puzzle)