Not causing harm obviously includes not killing or robbing or lying to people. It also includes not being aggressive – not being aggressive with our actions, our speech, our minds etc. Learning not to cause harm to ourselves or others is a basic concept teaching on the healing power of nonaggression.
Not harming ourselves or others in the beginning, not harming ourselves or others in the middle and not harming ourselves and others in the end is the basis of enlightened society. This is how there could be a sane world. It starts with sane citizens and that is us. The most fundamental aggression to ourselves, the most fundamental harm we can we to ourselves, is to remain ignorant by not having the courage and the respect to look at ourselves honestly and gently.