2 Timothy 1:7

For God have not given us a spirit of fear, but of power and of love and of a sound mind.

Sometimes it is just the little things that wear on our thoughts.  Something we should cast down, but we let a small offense, frustration, inpatients, sadness to plant a seed in our thoughts.  It could be a simple fear of losing the keys, and we know there is no proof to believe this imagination is real.  God did not give us a spirit of fear but a sound mind.  Combat those thoughts with the word before they become a hill, a stream and then a mountain to cross.