It is written that faith the size of a mustard seed is sufficient to do some pretty kick-ass stuff.
"And the Lord said, If ye had faith
as a grain of mustard seed, ye might say unto this sycamine tree, Be
thou plucked up by the root, and be thou planted in the sea; and it
should obey you." (Luke 17:6)
"And Jesus said unto them, Because of your unbelief: for verily I say unto you, If ye have faith as a grain of mustard seed, ye shall say unto this mountain, Remove hence to yonder place; and it shall remove; and nothing shall be impossible unto you." (Matthew 17:20)
"And Alma and Amulek came forth out of the prison, and they were not hurt; for the Lord had granted unto them power, according to their faith which was in Christ. And they straightway came forth out of the prison; and they were loosed from their bands;
and the prison had fallen to the earth, and every soul within the walls
thereof, save it were Alma and Amulek, was slain; and they straightway
came forth into the city." (Alma 14:28)
Even my faith was at least the size of a mustard seed (I actually like to think it was much bigger), but I was never able to work a miracle of any discernible magnitude.
The truth is I've never heard of any of this kind of thing happening in real life - only in scriptures and fantasy novels - and I think the Mormon Church (and other churches) have more than a few adherents who are sure "beyond a shadow of a doubt" of their beliefs. They have the faith, so where are the miracles?
I have to doubt these words of Jesus because they simply haven't proven to be true in the slightest. It seems instead that if you have faith the size of a mountain you'll be grateful for every little mustard seed of hope you come across.