Politeness to others is usually born our of respect for the individual, which you learn as a child.
When you being treated with respect by other members of the family, you learn to respect them as well.
The self-esteem that results from being recognised in a unique way by people who matters the most to you, helps you develop the confidence to succeed later in life.
Politeness and consideration to others are the type of habit, that once its developed stay with you for the rest of your life.
While common courtesy is relatively insignificant in the grant scheme of things, it is reflection of more basic values.
More importantly, while you are developing a habit to respect others, you more likely will get respect from them.
Peace&Love
Miti