For a moment, think about the engine in your car. Think about the pistons, the cylinders, the valves, the camshaft, the crankshaft and the bearings. Think about all these things as you are traveling down the highway at 75 miles per hour at night, in a blizzard with your family in the car. Think about how precisely things need to fit together, and how much you depend on the reliability of your engine. Think about the attention and care that was given when the engine was assembled.

Now assume that you own a car that was used when you purchased it. Further assume that the engine had been rebuilt sometime, while the prior owner had it. Now think about the attention and care that the engine was given when it was being rebuilt.

Compare the mental image you had of the first assembly of a new engine with the image you had of the engine being rebuilt. What were the differences, or do you believe that both procedures were substantially the same? Were the bearings replaced? How were they fitted to the shaft? Were the pistons replaced? How were the replacement pistons chosen? Was there an effort made to ensure they were balanced? How much wear was present on the surfaces of the camshaft? Were the valves worn? What was the condition of the valve springs? For that matter what did each person performing the work look like? Did the mechanic have clean hands when assembling precision components?