I'm working on the tech side of a company, and the business side sometimes asks for things that cannot be done. Yet, I never want to say "XYZ is impossible". Maybe it's possible but it would take 20 years to do, or maybe it's simply not worth my time (as I have 10 other higher-priority tasks to complete).
How do you diplomatically smooth over these issues?
Is inaction or deferring to later dates OK?