If the electric can opener were no longer followed by the food, the link between the sound of the electric can opener and food would become extinct. If the electric can opener were again followed by the canned food, the connection would then be reestablished and the link would be reconditioned. Reconditioning takes less time to pair the unconditioned stimulus and conditioned stimulus than the initial conditioning. In this example, electrical shock and money are both reinforces even though one is considered unpleasant by most. Sometimes our perceptions are faulty.
Humans use relative size to judge the size of the moon.
This is why the moon seems bigger and closer when it is near the horizon than when it is high in the sky. When the moon is higher in the sky there are no known objects or frame of references to judge the moon's closeness, and thus, appears smaller and farther away. This is called the lunar illusion. For example, a weight scale can be judged reliable if measures for a 25-pound weight do not vary over time or change for subsequent weightings. Reliability is an important concept in science.