eg. A human might not be expected to know too much medical terminology, hence could easily get names/locations/functions of muscles and organs mixed up. Whereas a computer might be brilliant at that, but then suddenly not know what a door knob is (door handle? door knob of butter? etc...)
So ultimately to make a computer seem intelligent the problem is two-fold: Getting a high percentage of right answers, whilst also getting the "right" wrong answers.
Afterall, we don't criticize a human too much for not knowing something like the exact geographic location of a small African nation. But we definitely would if they thought that it was on Mars! It's exactly the same with computers, they're just far more likely to make wildly incorrect mistakes than understandably incorrect ones. So finding a way to mitigate computer mistakes, to make them milder, is every bit as important as eliminating them entirely - a potentially impossible task.