Translation:You yourself do not believe what you speak.
Actually, "a vorbi" translates to "to speak". There is a little difference between "a zice" și "a vorbi". The first one means that you pronounce words or phrases, while the second one implies that there is a listener that listens to you and some kind of interaction between you and him/her. However, I doubt anybody will notice this subtle nuance between the two words in casual speech.