Romans 15:23

But he who doubts is condemned if he eats, because it is not from faith, for whatever is not from faith is sin.

Our thinking can be our downfall.  The devil knows this, and that is why he works to distract us with fears and worries.  Faith prays over something and then leaves it be.  Fear keeps talking about the problem and tells others until the fear becomes more significant than our faith.  We should cast down those imaginations that exalt above the word of God and rest in Faith.