My favorite response when Product Managers bring up that business needs to know when a feature will be done is "And I would like to know Apple's stock price in

My favorite response when Product Managers bring up that business needs to know when a feature will be done is "And I would like to know Apple's stock price in 6 months." I really believe this accurately communicates how difficult it is to estimate software development timelines. You can't estimate unknown work, and unless you're building wordpress blogs, your work in software is unknown.