We are only subject to a negative thought or belief if we consciously say that it applies to us.
For negativity to apply to our life, we must first subscribe to it and, secondly, give it the energy of belief. If we have the power to make negativity manifest in our life, obviously our mind also has the power to make its converse come true.
For more details on this passage: Letting Go: the Pathway of Surrender book, pg. 62-63