The best patterns have the same quality about them. An exemplary pattern is the Leaky Bucket Counter. Instead of describing the pattern let me tell you the story of the System Admin Sam.

Sam worked the night shift at a Telephone Switching center, to put himself through college. His job was to watch the transmission lines for errors, and take them out of service when they went bad. When a circuit had an error the monitoring station would beep for him to investigate. Most of the time it was just a random environmental event and nothing needed to be done. If the same circuit got a whole bunch of errors in a short period of time the error was probably real and the circuit should be shut down.

Since only once or twice a week a circuit would go bad, Sam tried to sleep. Unfortunately the random false alarms every 10-20 minutes kept Sam awake. So he devised a plan.

He rigged the alarm to squirt a little water into a bucket instead of beeping. Then he poked holes in the bottom of the bucket so the water would slowly drain out. The bucket would only fill up if the errors came quicker than the bucket could drain. By carefully placing the bucket so it would tip over when it got full, Sam could sleep during shift confident that a real error would quickly cause a full bucket of water to wake him up.

This story is made up, but the story, real or imagined, is what makes the best patterns.