Seven

Why is the number seven thought lucky?
Why, when a person picks a number between one and ten, is it so often seven?
Why are there seven deadly sins? Why only seven?
Is that in any way related to the fact that there are seven sacraments of the Catholic Church?
I just googled "number seven"- Why is seven so used in scripture?
Wow... I can't believe this wasn't the first question- Why are there seven days of the week?