The idea you're putting forth is to create an expectation that we can never accomplish in waking life in order to motivate our mind to solve the problem while in the dream: open the box. Is my understanding correct?

If it is, what is the difference between the closed box and desiring to fly. I'll never fly in this life, as far as I know, so would holding onto a longing for flying create the same psychological crisis that would instigate dream resolution? If I understood you correctly, it's not the closed box per se but the unrequited desire that brings about action by the subconscious in the dream.

Thanks for sharing the technique.