One day, a man pushed his car into a mechanic's workshop, and told the mechanic that he couldn't get the car to start.
The man was intelligent and well educated, and knew that cars worked using an internal combustion engine, to ignite a mixture of petrol and air, driving pistons in the engine to turn an axle and then the wheels of the car.
He watched the mechanic at work on his car, interested to see him dismantling pieces of it and examining them in some detail.
After a time, the mechanic came to the man and said that he was afraid that the throttle valve in the carburetor had cracked, and that he would need to order some new parts to fix his car.
The man was worried about this, because although he had heard about a carburetor, he didn't fully understand what it did - and he had certainly never heard of a throttle valve. He was suspicious that the mechanic was trying to rip him off, because as far as he was concerned, the internal combustion engine simply mixed fuel and air, ignited them, drove pistons and turned an axle and wheels, and this didn't sound complicated. Certainly his understanding did not include carburetors and throttle valves.
The mechanic explained that he had been trained very well in the rather more complex intracacies of how an internal combustion engine worked, and had many years' experience in how they functioned and how they could be fixed.
But the man was an intelligent man, and told the mechanic that his explanation was wrong and that it must be the case that something was preventing the fuel and air mixing, igniting, driving the pistons and turning the axle and wheels.
The mechanic patiently explained that yes, this was the case, due to the cracked throttle valve in the carburetor, but because the man did not know what a throttle valve was (and had only an outline of an idea of what a carburetor was), he continued to believe that the mechanic was trying to rip him off, and insisted that the mechanic was wrong and that it must be the case that something was preventing the fuel and air mixing, igniting, driving the pistons and turning the axle and wheels.
This discussion continued for many fruitless hours, until eventually the mechanic gave up, and the man left the mechanic's workshop, satisfied that he had avoided being ripped off.
And the moral of this story ? The mechanic (and the rest of his intelligent customers, who knew very little of carburetors and throttle valves, but who trusted the mechanic that he did) drove away that evening and went to many interesting and entertaining places. The man and his car, though, remained stuck in the workshop, feeling happy that they hadn't been ripped off, but going nowhere.