Malice

Never ascribe to malice that which is
adequately explained by incompetence.
- Napoleon

How much pain they have cost us,
the evils which have never happened.
- Thomas Jefferson

Do not anticipate trouble,
or worry about what may never happen.
Keep in the sunlight.
- Benjamin Franklin

The world is not out to get you. It is very seldom that anyone intends to harm you. When the mail-order company sends you the wrong product, or your friend doesn't return your phone call, it is very unlikely to be malice. People are usually just doing the best they can - in their own fallible human way.

Further reading: How to Stop Worrying

Never Let Anyone Get Your Goat

Vengeance

Acceptance Makes a Great Relationship Even Better

The #1 Secret of Great Relationships