"People can be cruel, and they will be. People can hurt you, break your heart and they will. But only you can let them KEEP hurting you."
The saying goes, if a snake bites you once, it may be the snakes' fault, but usually when the snake bites you a second time, it is your fault. When we are in the vicinity of something that is potentially harmful, like a relationship with a dishonest person, or a person who has no qualms with hurting us to get what they want, and they eventually do, it may not be our fault the first time that they do so, even if the warning signs were there.
It is only after these people hurt us and only when we choose to allow them into our lives to hurt us again, is it our fault that we get hurt again. As this passage says, people can be cruel, and they will be. This is not to say, that everyone will hurt you over and over again, and that no one deserves a second chance, but those who are chosen by you to receive a second chance, should be chosen wisely, and only with your heart's discretion.
"Stop going back to the one who brings you more pain than happiness. It's not worth it to continue to invest your feelings into somebody unworthy of your love. Everybody deserves second chances, but not for the same mistakes."