"Trust thyself" refers to the self-motivational mindset that tells a person to listen to their instincts, mind and heart. Ralph Waldo Emerson said in "Essays," "Trust thyself: every heart vibrates to that iron string." This quote speaks to trusting one's own feelings and avoiding conformity, because choosing conformity sacrifices independence.
One can find a number of references to "Trust thyself" in Western literature. A similar quote from William Shakespeare, "To thine own self be true" continues the positive affirmation of trusting oneself. This quote means that only through self-examination can a person make the best decisions and avoid relying on others to make those decisions.