Optimism is a wish without warrant (J. I. Packer, Canadian theologian).
Optimism helps a lot of us face the difficulties that arise in our experience with a positive outlook on life, hoping for the best. Packer continues: “Optimism hopes for the best without any guarantee of its arriving and is often no more than whistling in the dark.” He offers a better outlook: “Christian hope is a certainty, guaranteed by God himself.”
So God has given both his promise and his oath. These two things are unchangeable because it is impossible for God to lie. Therefore, we. . . can have great confidence as we hold to the hope that lies before us (Hebrews 6:18).