"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." (Mark 11: 23)
Not doubting in our hearts is a key provision of "you will have what you say," some would argue.
Yet the previous verse makes it clear that this kind of faith is God's faith, not ours, and we receive this faith through Jesus Christ.
The one work is to believe on Jesus (John 6: 29), and to the extent that we face any struggles, to the degree that we face hardships which appear insurmountable, to that extent our understanding of Jesus and His grace in our lives needs to grow (2 Peter 3: 18)
Paul prayed that everyone of us would see all that we have in Christ (not in ourselves, and certainly not in what we say):
"17That the God of our Lord Jesus Christ, the Father of glory, may give unto you the spirit of wisdom and revelation in the knowledge of him: 18The eyes of your understanding being enlightened; that ye may know what is the hope of his calling, and what the riches of the glory of his inheritance in the saints, 19And what is the exceeding greatness of his power to us-ward who believe, according to the working of his mighty power" (Ephesians 1: 17-19)
This understanding grows as we understand how much God loves us in Christ (Ephesians 3: 16-19)
He is established in our hearts, and therefore we are no longer busying ourselves trying to bring Him into our lives. Because we see the fullness of Jesus, and continue growing in grace, we stop asking God for things that we want, just because we are trying to get something else. Instead, He works within us to will and to do for His good pleasure (Philippians 2: 12-13), and thus we end up wanting the very things that Jesus wants us to want!
As you know Jesus, then indeed you will have what you say, because He will work in you the very things the desire to want things that He wants you to have!