Seven.

"All human actions have one or more of these seven causes: chance, nature, compulsions, habit, reason, passion, desire." ~ Aristotle.

Numerous books have been written about it. Fervent followers have ascribed a mystical significance to it. There are Oceans, Continents, Ancient Wonders of the World, Virtues, Sins, Dwarfs, Colors and Chakras that are said to add up to it. ~ It's the lucky number...

Scholars say that there have been only seven plots in stories and literature since the begining of time ~ Simply Seven Plots in life.

Tragedy.
Comedy / Romance.
Overcoming a Monster.
Voyage and Return.
Quest.
Rags to Riches.
Rebirth.

and apparently there are Seven Habits of highly successful people (Steven Covey)

Be Proactive.
Begin with the end in mind.
Put first things first.
Think Win-Win.
Seek to understand then be understood.
Synergize.
Sharpen the saw.

Seven Success Rules (Jack Canfield)

Take Responsibility and evict an entitlement mentality.
Identify and honor your purpose in life.
Decide what you want.
Don't complain, or blame, and believe anything is possible.
Be confident and have faith in yourself.
Expect opportunity, support and success.
Set and pursue goals.

and Bushido ~ The way of the Samurai ~ has Seven Virtues:

Rectitude.
Courage.
Benevolence.
Respect.
Honesty
Honor.
Loyalty.

We could go on and on...  For instance can you name the seven

Dwarfs.
Continents.
Seas.
Ancient Wonders.
Chakras.
Christian Virtues.
Deadly Sins.
Notes in a scale.
Ages of Man.
Colors of the Rainbow?

Or seven things you want to accomplish in the next seven days?