When did estimates turn into deadlines?

I've gone through times when management would treat estimates as deadlines, and were deaf to any sort of reason about why it could be otherwise, like the usual thing of them changing the specification repeatedly.

So when those times have occurred I've (we've more accurately) adopted what I refer to the "deer in the headlights" response to just about anything non-trivial. "Hoo boy, that could be doozy. I think someone on the team needs to take an hour or so and figure out what this is really going to take." Then you'll get asked to "ballpark it" because that's what managers do, and they get a number that makes them rise up in their chair, and yes, that is the number they remember. And then you do your hour of due diligence, and try your best not to actually give any other number than the ballpark at any time, and then you get it done "ahead of time" and look good.

Now, I've had good managers who totally didn't need this strategy, and I loved 'em to death. But for the other numbnuts who can't be bothered to learn their career skills, they get the whites of my eyes.

Also, just made meetings a lot more fun.

The hallmark of a bad manager who doesn't know they're a bad manager: "Why can't you just give me a number?" Inexperienced managers or people backfilling for someone else I can completely understand, they're not comfortable with the uncertainty they're dealing with. However in any other circumstance I think it's inexcusable.

But you have to remember that the manager is going to be asked for an estimate by his boss. He can't just say some time between "1 day and 10 years." In the real world, you have to be able to give some sort of estimate and help the poor guy do his job.

And thus we get to the root of the problem. As as business executive, why not simply track how long your big projects tend to take, rather than try and dictate how long they should take?

How can you tell what is worth doing if you don't know how long it might take?