Truly, I say to you, whoever says to this mountain, ‘Be taken up and thrown into the sea,’ and does not doubt in his heart, but believes that what he says will come to pass, it will be done for him.
Mark 11:23

"This mountain", not just any mountain. Yeshua wasn't saying that you can have anything you want if you believe strongly enough. He was making a specific prophetic statement concerning Israel. Either he was making an allusion to prophecies concerning the Mount of Olives or he was speaking of the Jewish leadership. Maybe both.

In either case, God's consent is contingent on the request being in accordance with his will. He desired to whither the fruitless tree of first century Judaism and replace it with a new leadership structure centered on the Apostles, and that is exactly what happened.