(Mark 11:24) Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them.
Certainly there are examples of people doing amazing miracles.
(Acts 3:6,7) Then Peter said, Silver and gold have I none; but such as I have give I thee: In the name of Jesus Christ of Nazareth rise up and walk. And he took him by the right hand, and lifted him up: and immediately his feet and ankle bones received strength.
Jesus seems to promise that we can do anything no matter how frivolous.
(Mark 11:23) For verily I say unto you, That whosoever shall say unto this mountain, Be thou removed, and be thou cast into the sea; and shall not doubt in his heart, but shall believe that those things which he saith shall come to pass; he shall have whatsoever he saith.
Certainly there are Saints who are known to be miracle workers. But no one has ever cast a mountain into the sea. Various reasons are given for this failure:
Performing miracles seems to be a gift from God — there is nothing we can do to receive this gift. Some Saints had this gift, others not. The ability to perform miracles did not make someone a better Saint or a more saintly person.
(Mark 2:5) When Jesus saw their faith, he said unto the sick of the palsy, Son, thy sins be forgiven thee.
The only faith these required was a strong conviction that Jesus was a miracle worker and the determination to get the sick man into Jesus' presence. They didn't have to believe in any supernatural "faith power" within themselves.
Paul (himself a miracle worker) indicates that not everybody is to be a miracle worker.
(1 Corinthians 12:10,11) To another the working of miracles; to another prophecy; to another discerning of spirits; to another divers kinds of tongues; to another the interpretation of tongues: But all these worketh that one and the selfsame Spirit, dividing to every man severally as he will.
One difficulty is that linking faith with miracles makes us wonder whether we have enough faith to be saved. If we don't have enough faith to do the less significant thing (throwing a mountain into the sea) how can we be sure that we have enough faith for the most important thing (receiving the gift of salvation?)
(Matthew 14:28-31) And Peter answered him and said, Lord, if it be thou, bid me come unto thee on the water. And he said, Come. And when Peter was come down out of the ship, he walked on the water, to go to Jesus. But when he saw the wind boisterous, he was afraid; and beginning to sink, he cried, saying, Lord, save me. And immediately Jesus stretched forth his hand, and caught
Peter initially had adequate faith, then he wavered, then Jesus caught him, presumably miraculously. Peter sincerely desired to commune with Jesus out on the waves but when he got distracted his faith failed him. Faith requires focus. The same holds true for saving faith — we must focus every aspect of our lives on the goal of eternal redemption and worship of the Creator.
I believe the solutions to these problems are as follows: