The sum of what Jesus taught in Mark 11:23 concerning the subject of faith is found in Paul’s letter to Timothy:
“Fight the good fight of faith…” 1 Timothy 6:12
Fight! Anybody can say anything but it’s the tenacity to stick to what has been said despite contrary and rebellious circumstances that exhibits faith.
Remember, faith is the evidence of what you already have, so no matter how anybody tries to talk you out of it, as long as you have the evidence you know they’re lying.
And what faith this woman whose daughter was afflicted by a demon had:
“And she said, Truth, Lord: yet the dogs eat of the crumbs which fall from their masters’ table.” Matthew 15:27
This was in response to a statement Jesus had made that could have come across as insulting and dissuaded her from what she was asking for but instead she fought! Refused to let what could have been a set back affect her, instead found an opportunity in it and she got what she wanted and how impressed Jesus was with her:
“Then Jesus answered and said unto her, O woman, great is thy faith: be it unto thee even as thou wilt…” Matthew 15:28

Bible Reading Plan: Ecclesiastes 2 and Numbers 15