This. Very few problems are truly impossible to solve, they arem in fact, just wildly impractical to solve. So don't try to tell the PM/client/coworker-with-a-'brilliant'-idea it can't be done, tell them what it'll take to work out what it'll take to do it. Either they go away, or you end up in charge of a project with an astronomical budget and no clearly defined deliverables.
This. Very few problems are truly impossible to solve, they arem in fact, just wildly impractical to solve. So don't try to tell the PM/client/coworker-with-a-'brilliant'-idea it can't be done, tell them what it'll take to work out what it'll take to do it. Either they go away, or you end up in charge of a project with an astronomical budget and no clearly defined deliverables.