Positive thoughts = Positive outcomes

You can have a negative experience without having a negative thought. A negative thought divides you.  The Bible tells us, "a house (or in this case a brain) divided against itself cannot stand." You are your own worst enemy. If you allow yourself to be divided, you allow yourself to be conquered. Be steady in your feelings about yourself and your situations. If David had allowed himself to think that he could not face Goliath, Goliath would have surely conquered him. David was steadfast in his belief in himself and his God, you must be also. We all face situations that seem like they are not going to work in our favor, but favor is yours for the taking; dont take yourself out of favor thinking negatively about yourself or the situations you find yourself in.
Negative situations often make us doubt or question God. God has a plan that you cannot see or understand the reasoning for, this is where faith and trust in Him is tested. Trust in God always. Be full of faith at all times.