When you decide that things outside your control are good or bad, you set yourself up for trouble. If you think something you can't control is good, you'll be upset when you don't get it. If you think something you can't control is bad, you'll be upset when it happens to you. Either way, you'll end up blaming the gods and hating other people. You'll blame whoever caused you to miss the good thing or fall into the bad thing. This way of thinking leads to many wrongs. We do harm when we care too much about things that aren't really up to us.
What things soever are not within the proper power and jurisdiction of thine own will either to compass or avoid, if thou shalt propose unto thyself any of those things as either good, or evil; it must needs be that according as thou shalt either fall into that which thou dost think evil, or miss of that which thou dost think good, so wilt thou be ready both to complain of the Gods, and to hate those men, who either shall be so indeed, or shall by thee be suspected as the cause either of thy missing of the one, or falling into the other. And indeed we must needs commit many evils, if we incline to any of these things, more or less, with an opinion of any difference.