In Christian churches, there is often exhortation that our faith in God be strong. Some denominations emphasize this to the point where, if a desired miracle does not occur, it is a problem of weakness or lack of faith. Yet Galloping Gertie has something to teach us about faith, to wit: the power of faith resides in the nature of its object, not in the strength of belief in the object.
There can be no doubt that Leon Moisseiff had unshakeable faith in the reliability of his newly-completed masterpiece, and would have had no qualms whatsoever driving over it in any weather conditions. Yet had he been on the Narrows Bridge on November 7th 1940, his faith would have been fatal to him. The object of his faith proved unreliable, and the strength of his faith irrelevant.
Yet there is another common problem with faith, which can be equally fatal: the unwillingness to act on that which is reliable because of doubt, fear, or pride. After the second Narrows Bridge was completed in 1950, many people were understandably reluctant to drive on the new span. Had a life-threatening emergency arisen demanding a trip across the bridge, such fear would have proven equally fatal, although the bridge was entirely reliable and capable of supporting such transport.
Jesus spoke of faith the size of a mustard seed moving mountains. The lesson is not about seeds or mountains, but rather intended to express the truth that a tiny amount of faith in an infinitely powerful God is vastly more efficacious than unlimited faith in the unreliable. Yet for faith to function, action is required, based on trust in the reliable nature of its object. Such faith, though fearful and timid, has power, and builds the foundation for greater faith based on experience.