David Livingstone
Reading David Livingstone's story did not interest me much. However, what I found interesting was he realized that he needed to travel into the deepest parts of Africa to develop trade. Africans could receive goods to help eliminate slavery, and also so they could hear the gospel.
What does strike me about David, is that he did not have much success in the way many people would think. His converts were few and yet he did what God led him to do. Eventually his faithful work opened trade routes never opened before and his story was told around the world. He is perhaps one of the most famous missionaries of all time.
Never doubt God. When you feel as if you are not making a difference: think of David. He simply obeyed and let God deal with what seemed like failure. God instead made it great success. He delights in making greatness in apparent failures.