Ever looked up at someone because of their unshakeable faith? Ever asked God for greater faith? I like what Jesus said about it in Matthew 17:20 (TEV),
I assure you that if you have faith as big as a mustard seed, you can say to this hill "Go from here to there!" and it will go. You could do anything!
Notice that this translation says faith as BIG as a mustard seed. Jesus' perception of size is different than ours! He basically tells the disciples, and us today, what mustard seed faith is: something very small you can use in order to do something very big! Go ahead, use what He has given you!