In one job, I had a fantastic boss who was incredibly clever, but had no common sense. He was like an absent-minded professor. He used to cycle the mile or two to work, and swap tracky bottoms for suit trousers when he got into the office.
One morning, he got a phone call first thing and got engrossed in whatever it was about, then called his secretary in to take dictation (this sounds almost Dickensian now, but it was only the early 90s). At some point, he paused in whatever he was dictating and got up to check something in a file.
He wasn't wearing any trousers! He'd got interrupted after removing his tracky bottoms and before putting his trousers on, and completely failed to realise he was sitting there in his pants. 
An anotehr occasion, I was in the secretary's room when she sent an urgent fax to someone in another department, about a 20 minute walk away, for him. A few minutes later, he came in and said "Goodness, that was amazingly quick. X has just rung me, and he's got that document already". It transpired he thought faxing was some sort of superfast courier system, and it did his head in when we tried to explain it was all electronic.
Late one afternoon, the secretaries had gone home and I was finishing off some work when he wandered in looking all perturbed. He wanted some last minute revisions done to a huge document that he needed for a very early meeting the next day. I explained that I could do it for him if said document was in one of the common directories, but not if it was in his own, as I didn't have access to that. He couldn't grasp this at all.
Eventually I resorted to analogy, and said "It's as though all the work is in different cabinets. I have keys to some of the cabinets, but not to others".
"Ahhh", he said, as the light appeared to dawn. "You'll have to show me where the keys are kept".
He was a lovely man, and one of the best bosses I have ever had: easygoing, kind, very supportive and scrupulously fair. And despite being something of an innocent abroad, he was a brilliant lawyer whose written advice was always a model of clarity. I was gutted when he took early retirement.