When dealing with the Negative Nancy's and Petty Betty's, you truly have to stand firm on what you know and believe about yourself! If you don't know how to motivate and push yourself, they will take you down.
As it says in the Bible in Matthew 12:34 KJV, "For out of the abundance of the heart the mouth speaketh." The New Living Translation breaks it down a little simpler and says, "Whatever is in your heart determines what you say." Simply put, if you're thinking it, you're going to say it.