Looking to scriptures for the answer, we see that Jesus battled the same thing, a great example is in Matthew's gospel the 17th chapter. Jesus, Peter, James and John had just come down from the mountain where Jesus was transfigured into the fullness of His divine glory right before them.
As the four of them descended from the mountain a man came up to Jesus and asked Jesus to heal his son who was tormented by seizures and lunacy, stating that he had brought him to his disciples and they could not heal him. Look at Jesus' response... "You unbelieving and perverted generation, how long shall I be with you? How long shall I put up with you? Bring him here to Me.' And Jesus rebuked him, and the demon came out of him, and the boy was cured at once. '' ( Matthew 17:17-18 )
Not the response one would expect from Jesus. In our current mindset, we would expect Jesus to say something like 'well of course I can heal him, bring him to me', But he didn't, he rebuke the people for their unbelief even before he rebuked the demon that seized and tormented this boy. The Gospel of Mark gives us a little more detail about this account. After the boy had been brought to Jesus, the spirit within the boy threw him down and into a convulsion, foaming at the mouth. Then the Father said to Jesus, "if You can do anything, take pity on us and help us!" ( Mark 9:22 ).
Now Jesus had just rebuke the people and the disciples for their unbelief and called them a faithless and perverse generation because they had seen and heard of the countless miracles performed by Jesus and still did not believe. And now the father who is desperate for his son to be set free, states to Jesus, 'IF YOU can do anything, help us' and look at Jesus' response, "And Jesus said to him, 'If You can?', [question mark] 'All things are possible To Him who believes." [Explanation point!]
Notice, the man goes to the disciples for them to heal the boy, when they cannot, he goes to Jesus and prefaces his request with doubt and unbelief. 'If You can...' Jesus' response was basically stating to him, that all things are possible to him to believe. He didn't tell the man, 'yes I can heal him', he told him all things are possible To Him to believe. The difference between the man, the crowd, the disciples and Jesus, is that Jesus believed... and all things were possible because of that.
At this point, the struggling man recognized that unbelief cancels out faith, and had the sense to state his faith and ask God to help him with his unbelief. The Amplified Bible says it this way, 'At once the father of the boy gave [an eager, piercing, inarticulate] cry with tears, and he said, Lord, I believe! [Constantly] help my weakness of faith!" ( Mark 9:24 )
And because of it the Lord drove out the demon, healing and restoring the boy and encouraging the Father is his Faith. And just as unbelief nullifies Faith, the opposite is true, Faith cancels out doubt.
It isn't popular to say, that a person didn't get healed because of their lack of faith or the lack of faith of the person praying for them. No one wants to take personal responsibility for it, but in this case, Jesus rebuked the people for their lack of faith when the boy was not healed. They had tried to heal him, and we expect Jesus to give them an A for effort, but instead he was harsh with them when they failed and let their doubt control the situation, saying, 'ALL THINGS are possible to him who believes.'
Later on when the disciples were alone with Jesus, in Matthews account, they asked him why they could not drive the demon out. And again, Jesus' response was because they had so little faith. But just so they knew the amount of faith that they need to accomplish this, he went on to tell us an amazing truth. Matthew 17:20 says, "And He said to them, "Because of the littleness of your faith; for truly I say to you, if you have faith the size of a mustard seed, you will say to this mountain, 'Move from here to there,' and it will move; and nothing will be impossible to you." the Amplified Bible calls it 'Faith that living like a grain of mustard seed'
Jesus said' if you have faith as small as a mustard seed nothing will be impossible for you' and we hear and 'if you have faith as great as a mustard seed this will work five percent of the time', and that is why we get the results of the crowd and not the results of Jesus.
In Mathew 13:31-32, Jesus used the example of a mustard seed again, this time when explaining what the kingdom of heaven was like... "The kingdom of heaven is like a mustard seed, which a man took and sowed in his field; and this is smaller than all other seeds, but when it is full grown, it is larger than the garden plants and becomes a tree, so that the birds of the air come and nest in its branches. "
See when Jesus told us that we need living faith the size of a mustard seed, it was because he knew that once that seed took place and rooted and became established, it would become the largest of garden plants and grow into a mighty tree. And when that happen life's circumstances and the trouble of this world can perch in our faith and we remain unmovable. Jesus said, when you have faith like that, then the mountain moves.