Impossible is good. Impossible gets the creative juikces going. In fact, companies not trying the impossible are doomed, I think, either from business or from a creative point of view.

Too often, the CEO will ask you to do something that would have been easy had they picked up the right signals 6 months ago, or given the right resources, or whatever. That will definitely make engineers shrug and think: I'd better start editing my resume.

It should however be the kind of impossible that makes you think "YES", that's what we need, if we could do that, that would be so cool, yes, I'm willing to sacrifice the next 6 months of sleep and social life, because if we make it, we really achieved something memorable.

Many engineers are very much motivated by impossible stuff. Space travel, Large Hadron Colliders, iPhones. It's wat makes us tick.