God was faithful and gave Isaac to Abraham and Sarah a year later. Abraham was faithful to obey God, and he was blessed for his devotion. This tenacity for glorifying God in all pursuits is why Paul so vehemently made himself a slave to all men in hopes to save some to salvation in Christ. Olympic athletes don't just start with the goal of becoming an Olympian. That might be their broader vision, but each step of the way involves a faster time, a higher jump, or a flawless technique.
Progress takes time.
Be willing to take risks. God asks that we trust Him despite our limited understanding. He makes progress only when he sticks his neck out. If God has given you a clearly defined goal and you sincerely believe it to be His will, don't let doubt or discouragement defeat you. Remember that the process is the greatest learning experience we have.