We can get involved in missions expecting great things from God. We can go with the confidence that He is going to save people from every people group of the world. Our boldness in attempting great things for God should be based on our knowledge that He is going to accomplish great things.
Remember Carey's motto. Begin with prayer, asking God to do great things in your own life and in the lives of others. Then act on those prayers, attempting great things for God as you expect great things from Him.