Bob quotes John Stuart Mill

any one who feels it conducive either to his satisfaction or to his usefulness to hope for a future state as a possibility, there is no hindrance to his indulging that hope” (Mill 1874: 210).

and

L1. For all one knows or justifiably believes, the object of one’s hope could obtain; and,
L2. One believes that hoping contributes to one’s own happiness, or to the well-being of others.

and agrees with him that

there is practical good if it helps you to be happy, or if it helps in the happiness of others

I found a similar quote by Brad Billy-Bob Mill that makes a similar claim about the ability to fly. If I concentrate very, very hard I can levitate several hundred feet in the air. I have never actually levitated because I have not yet concentrated hard enough but I am sure I will one day. Even if it’s not true and I will never actually be able to prove it one way or another, the belief that I will makes me happy. It contributes to the happiness of my friends. Therefore I am justified in believing that I can fly.