Doubt is a choice.

I am seeing in my life and the lives of other believers that when we are tempted and when we fail, those moments are not moments where we doubt that God is real or powerful.  Those moments are moments when we choose to believe that we know what is better for ourselves than does God.  It is a rejection of His authority, and a doubting of His goodness rather than a doubting of His existence and ability.

¹⁸ And a ruler asked him, “Good Teacher, what must I do to inherit eternal life?” ¹⁹ And Jesus said to him, “Why do you call me good? No one is good except God alone. ²⁰ You know the commandments: ‘Do not commit adultery, Do not murder, Do not steal, Do not bear false witness, Honor your father and mother.’” ²¹ And he said, “All these I have kept from my youth.” ²² When Jesus heard this, he said to him,“One thing you still lack. Sell all that you have and distribute to the poor, and you will have treasure in heaven; and come, follow me.” ²³ But when he heard these things, he became very sad, for he was extremely rich. ²⁴ Jesus, seeing that he had become sad, said, “How difficult it is for those who have wealth to enter the kingdom of God!²⁵ For it is easier for a camel to go through the eye of a needle than for a rich person to enter the kingdom of God.” ²⁶ Those who heard it said, “Then who can be saved?” ²⁷ But he said, “What is impossible with man is possible with God.” ²⁸ And Peter said, “See, we have left our homes and followed you.” ²⁹ And he said to them, “Truly, I say to you, there is no one who has left house or wife or brothers or parents or children, for the sake of the kingdom of God, ³⁰ who will not receive many times more in this time, and in the age to come eternal life.”  – Luke 18:18-30, ESV

In this passage Jesus is affirming His own goodness and His own deity.  Just like the lesson of the rich young man, we must trust Him even when we don’t want to.