Here are 7 reasons why we apparently like the number 7 ...
1. 7 is magical. The religious and spiritual associations to the number 7 go back through the millennia, ranging from the 7 deadly sins to seventh heaven. The ancient world was declared to have 7 wonders in it although there were obviously countless others that deserved this designation.
2. 7 is lucky. The prototypical lucky number, 7 is a heavy hitter in the gambling world. Slot machines often offer three 7's as the big payout. Our brain feeds off positive associations, and "Lucky 7" gives us an automatic preference for the number itself.
The next three reasons relate to 7's quality as a number:
3. 7 is a good playoff number. You will never have a tie when there are seven events needed for a deciding outcome. When 5 doesn't seem like enough and 9 like too much, 7 is the perfect halfway point.
4. 7 occurs throughout nature. There are 7 seas, 7 continents, 7 colors in the rainbow, and 7 days of the week. The number 7 has interesting properties, including the fact that it's the total of all opposite sides of a single die.
5. 7 sounds good. As NPR commentator Frank Deford pointed out, 7 is the only single digit number that has two syllables. "Snow White and the Seven Dwarfs" rolls off the tongue. "Snow White and the Eight Dwarfs" just doesn't work quite so well.
The final 2 reasons involve our brains and the way we process information. We may literally be programmed to like the number 7 because our brain is hard-wired to clump things in 7's.
6. 7 is the size of a memory chunk. The psychologist George Miller observed many years ago that our short-term memory remembers in units of 7 plus or minus 2. You can remember an infinite list of words, tasks, or facts if you organize it into 5 to 9 (but ideally 7) chunks.
7. 7 is a neuron's favorite number. For years, scientists were mystified about the reasons for Miller's "magical number 7 (plus or minus 2)." Now we may know why. A 2008 study on neurons in the memory input unit of the brain, the hippocampus, showed that they produced the best information when their dendrites (the branches that receive stimulation) numbered 7. Perhaps we remember best in 7's because that's what our brains are best able to store.
http://www.psychologytoday.com/blog/fulfillment-any-age/201109/7-reasons-we-7-re...