Marcus: The soul of a man does violence to itself, first and foremost when it becomes so far as in it lies, a separate growth, a blain as it were upon the Universe. For to turn against anything that comes to pass is a separation from Nature, by which the natures of each of the rest are severally comprehended. Secondly, when it turns away from any human being or is swept counter to him, meaning to injure him, as is the case with the natures of those who are enraged. It violates itself, thirdly, when it is the victim of pleasure or pain; fourthly, when it acts a part, and says or does anything both feignedly and falsely. Fifthly, when, failing to direct any act or impulse of its own upon a mark, it behaves in any matter without a plan or conscious purpose, whereas even the smallest act ought to have a reference to the end. Now the the end of reasonable creatures is this: to obey the rule and ordinance of the most venerable of all cities and governments.
Me: A person does herself injury when, firstly, she strives against or abhors anything that's happened. This goes against nature and will incur the pain of separation from reality. Secondly, by being always angry at others, blaming them and wanting to hurt them, she will cause herself pain. A person who, thirdly, allows either pain or pleasure to overcome her and, fourthly, says or does to others what she doesn't believe in or knows to be false, does herself and injury. Fifthly, she hurts herself when she behaves carelessly or impulsively and doesn't adhere to goals. She should always keep to her plan. Finally, a reasonable person will follow her area's customs and the government's laws.
See also this entry.