The failure named here is not weakness but the refusal to trust the one power the mind actually has. Even the smallest willingness, no larger than the least of seeds, is enough, because it is not the size of the faith that moves things but the truth it rests on. A mind that believes the obstacle is solid keeps it solid; a mind that grants even a little trust to love finds the obstacle was never as real as it looked.
The mountain is any barrier the ego calls immovable, and it stands only while the mind agrees that it must. Nothing is impossible not because effort is limitless but because the limits were imagined. To trust even slightly is to learn that what blocked the way was made of the same belief that can now let it go.
Mustard seed: the smallest measure of willingness to trust love, enough because its power lies in truth, not in size.
Mountain: any obstacle the ego declares immovable, solid only while the mind agrees it cannot yield.