Your mind will believe anything you feed it, so feed it faith. Feed it truth. Feed it love. As within so without. How you feel is reflected back to you in your reality. You manifest your life depending on how you feel, think and act in the real world as well as within the world that lives only in your mind.
If you are angry on the inside, then you will find yourself surrounded by fellow angry specimens including yourself.
If you could convince yourself of anything, what would it be? Why not convince yourself that you are happy? Your mind will believe anything you tell it if you feed it long enough, so choose the main course wisely.