What is the meaning of do your best and god will do the rest?

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. Therefore I say unto you, What things soever ye desire, when ye pray, believe that ye receive them, and ye shall have them. Mark 11:23,24

If a believer is praying for something in harmony with God's purposes, he should keep praying and believing for it, and not be dissuaded if the odds are stacked against him. We are to do our best to believe, realizing God will always do His part: the impossible and miraculous.