Seven?

Seven is number which has deep rooted significance for the human race regardless of culture:

The number of objects in the solar system visible to the naked eye — the Sun, the Moon and the five classical naked eye planets: Mars, Mercury, Jupiter, Venus, and Saturn.

The neutral pH - the pH level of pure water.

Seven days in the week.

God rested on and sanctified the 7th day

The number of heavens in Islamic tradition

The number of the Seven Deadly Sins: Lust, Gluttony, Avarice, Envy, Wrath, Sloth, and Pride.

The number of the Seven Virtues: Chastity, Moderation, Liberality, Charity, Meekness, Zeal and Humility, corresponding to the seven deadly sins.

In Buddhism, Buddha walked 7 steps at his birth.

In Khasi mythology, the seven divine women who were left behind on earth and became the ancestresses of all humankind

The number of gateways traversed by Inanna during her descent into the underworld

The number of sages in Hindu mythology. Their wives are the goddesses referred to as the "Seven Mothers"

The number of main islands of mythological Atlantis

Seven Lucky Gods exist in Japanese mythology.

The Magical Number Seven, Plus or Minus Two is a 1956 paper by cognitive psychologist George Miller who found a correlation between various human cognitive capacity limits within the range 7±2.

When asked to choose a number between 1 and 10, the most common number chosen appears to be 7. This choice appears to be driven by peoples idea of the properties a random number should have.

Other Models using the number seven:

The Seven Habits of Highly Effective People - Stephen Covey

Seven multiple intelligences (now 8) - Howard Gardner