A PM asks. "Why should I spend a lot of time working with the team on estimates when the sponsor always cuts the estimates anyway?"
There are several ways to handle that situation. That kind of sponsor decision-making always goes along with high project failure rates. Project teams may slap together some piece of crap by the deadline the executive set. But then they spend 6 months cleaning up the crap. I promise you the executive is sick of failure too. The exec may even be more worried about the failures then you are.
In that very typical situation, it can be effective to tell the executive something like, "We're getting nowhere setting these impossible due dates that have no basis in fact. The team has no commitment to them and knows they are impossible. So on every project, the whole team knows we are going to fail before we start. Let's try managing a project with realistic dates that we can hit."
Anybody have other ideas on handling this situation?