How do I stay hopeful and honest through scientific failure?

You hold scientific failure as the path itself, staying rigorous and hopeful without deceiving yourself about the data. That is the mature scientist's posture, and it is hard to keep. The pressure always runs toward either despair or wishful thinking, and you are refusing both. What you have understood is that hope and rigor are meant to work together, not against each other. Rigor without hope becomes cynicism and you stop trying. Hope without rigor becomes delusion and your work stops being worth anything. Held together, they let you keep pushing through failure while still telling yourself the truth about every result. Protect that balance with habits, not just willpower. Invite hard scrutiny of the results you most want to believe. State beforehand what would change your mind. And let yourself rest and recover, because staying both hopeful and honest over years takes more energy than either one alone. You are running a long race, and the honesty is what makes the hope worth anything.