The scripture in Matthews 17:20 speaks to faith the size of a mustard seed being enough to move mountains. The scripture has led many people to believe that if they believe just a little teeny winsy bit, God will be able to resolve the situation for the individual. There is truth to that. But God calls for us to have total unequivocal faith in Him.
How would you feel if someone told you that they only believed in you a little bit, not fully, just somewhat? It's not an encouraging feeling at all. God wants us to believe in him wholeheartedly. However, is belief in God just a little bit enough faith to move a mountain? Possibly. God can chose to work with you how he sees fit. We sometimes come up short a few cents at the store, but the cashier let's you go one with your purchase. I'm convinced God does the same.
However, revelation to the scripture can first be seen in natural things first before understanding spiritual things. For example, in order for a five ton wall to move, it needs a force greater than five tons. The force can come in pressure, speed, or mass. But anything less will not move the wall. The effectiveness of faith requires a faith greater than the obstacle in order to move the obstacle. How then can faith the size of a mustard seed move a moutain, an obstacle clearly a greater mass than the mustard seed (faith)? Answer: because no obstacle is too great for God, what may seem mountaneous to the individual is smaller than the size of a mustard seed in God's eyes. In other words, the mountain is smaller than the mustard seed. The faith has to be greater than the mountain, making faith the size of a mustard seed reflect the simplicty and effectiveness of God to resolve any situation, no matter the size, because the size (to God) is always smaller than a mustard seed.
Imagine that! What seems like a mountain to us is no bigger than a mustard seed to God. In and of itself that should be encouraging. It's important to have faith when resolving conflict. Faith helps to shepherd us through dark times as it reassures us that that universe will make things right. God is fair and just, and in time, all things work together for good for those who care, share, and love.