Or maybe they're parrots. If you're talking a mathematician and want to sound like you're making a valuable contribution, you can reasonably safely say something like "Perhaps you could use induction?" or "Why not use proof by contradiction?" Whatever they're doing, there's almost always _something_ to be gained by considering the induction, even if you already have, even if it cant' work :) (I don't think that actually has anything to do with your point, I just thought it was funny.)