Try Build a prototype. Mock-up if needs be. Present/"sell" it as idea to a limited circle (maybe starting with just you as user). Throw away.. most of it (the prototype, not the knowledge gathered). Rinse. Repeat. Several times. Every time decrease the freedoms, harden the model and narrow the focus, and expand the circle of surrogate-"users", slowly finding the eventual target (people or domain or point-of-pain). Eventualy involve marketing/management types as another kind of users (not of the thing itself, but of the process of it's creation). Note i did not mention "software". u can apply this to a Rough idea - it is also kind of virtual "software", but running inside someone's head.
Ah, and have fun.