The number 7 is common in the universe
There are 7 days in a week, 7 continents in the world, 7 seas, 7 colors in a rainbow, 7 wonders in the world and snow white was accompanied by 7 dwarfs.
Odd numbers are more appealing to the brain
Mathematician Alex Bellos, who did a research on the popularity of numbers, said that odd numbers are more appealing to the brain since a person believes that they have a special personality as a result of not being able to divide them by 2.
It’s the first number that can be rounded to 10 after 6
The human mind likes to round numbers to the nearest multiple of 10. Reaching number 7 for the human mind is like getting closer to 10 as it’s the first number that can be rounded to 10 after 6.
It is referenced in many religions
Many of the popular religions have references the number 7 such as Christianity, Judaism, Islam and Hinduism. The attachment to the number could be caused by the person’s desire to prove his religion correct.
It’s linked to many cultural beliefs
The ancient Greeks believed that 7 is a lucky number. In Ancient Japanese culture, people believed there were 7 Gods. The same was true in the Roman and Egyptian cultures. The number 7 was also referenced many times in ancient Chinese culture and given special importance.
Only 7 planets were visible in our solar system
When the telescope was first invented, only 7 planets were visible. This gave the number seven special importance and made it seem like it’s unique.
7 is considered a lucky number in gambling
In casinos, the slot machine is famously known for its lucky 7 where a person can win a big prize by getting three sevens together. (See Why is opening an umbrella indoors considered bad luck?)
Some religions believe the world was created in 7 days
Jews and Christians consider the number very significant because it refers, according to their beliefs, to the time God took to create the world. While Muslims do believe the number 7 is important, they believe the world was only created in 6 days or 6 phases of time that have different lengths.
If you roll two dice your chances of getting a total of 7 is the highest
If you roll two dice, the chance of getting a total number of 7 is 16.67% which is the highest possible percentage. Right after it comes 6 and 8 both with the probability of 13.89%. This might be another reason some people consider 7 a lucky number. (See Why is spilling salt considered bad luck?)
Some people suggest the brain can only process 7 bits of information at a time
Some scientists suggest that the brain can only process 7 bits of information at a given time. Those people say that a person can recall a maximum of 7 items and start to make mistakes if he is asked to memorize more in his short term memory.
It sounds good
Some people claim that the number 7 is popular because it sounds better than other numbers as it’s the only number consisting of two syllables.
The media leveraged the number’s popularity
The media & Hollywood leveraged the belief about the power of the number 7 by featuring it in the titles of many movies such as 007, Seven Years in Tibet, Se7en, The Magnificent Seven and Seventh Heaven.
Pythagoreans considered it a perfect number
According to Wikipedia, Pythagoreanism is a term used for the esoteric and metaphysical beliefs purported to have been held by Pythagoras. Pythagoreans called it the perfect number, 3 and 4, the triangle and the square, the perfect figures.
Why is 7 considered a lucky number by many people?
Is Seven Really a Lucky Number? Why ‘lucky 7’ really is the magic number?