Dont burn bridges

By that I mean maintain your relationships with people even if you think you are never going to see them again. For example, if you are quitting your job, dont chew out your boss before leaving, You might run into him her again later and life and wish you had never severed ties so harshly. You never know when you might need the help of someone you knew in the past. Plus there is already too much hatred in this world, why add more towards the people you interact with?