John....may I add one of my own favorite Bible passages...

Philippians 4:8 New International Version (NIV)

"Finally, brothers and sisters, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things."

Mark: Metaphysically speaking, Jesus was saying the mind cannot think of two things at one time (both positive and negative thoughts)!