Don't take anything for granted. Don't take anyone for granted. Don't ever think that you can do whatever shit to someone without he or she noticing it. Nobody's a fool. Even the person who kneels before the chair you sit on can have enough of it if you treat them as a trash.

Say sorry. For the major things. To the people who deserve it. Say sorry if you say something bad behind someone's back. Say sorry if you lose something that is not yours; or, if you take, for that matter.

Say sorry. For the minor things. For making someone wait for an hour. For losing your temper to someone who did not do anything. For making somebody feel like a total crap.

Say sorry, for they may understand. They may try and understand. But being treated as someone who doesn't deserve even the simplest 'sorry' can be, in the long run, be very tiresome. And most people doesn't like getting tired.