James 1:6

But he must ask (for wisdom) in faith, without doubting (God’s willingness to help), for the one who doubts is like a billowing surge of the sea that is blown about and tossed by the wind. 

We will doubt if we don’t know the promises of God. We will doubt if we haven’t discerned the voice of the enemy in our heads and take his suggestion as our thoughts. We will doubt if we don’t cast down the thoughts in the name of Jesus and believe the lie over the truth of the word. The wisdom and faith are ours and a promise of God, but we must take that promise by faith.