Unfeasible deadlines eat motivation.

I'm wondering how many such deadlines it needs until I'm incapable of doing anything.

It's crippling, right? The only thing worse are weekly progress meetings for something that would take months. And every week the same thing:
"Any progress?"
"Not really..."
And then we discuss the same thing over and over. Those meetings are a constant reminder of what I have not been able to do. :'(

@paranoidAndroid Yes.

If it's sure that a deadline cannot be met even if you're working your ass off, there is no sense in trying it anyway. Motivation just vanishes then and that makes it even worse.

It wouldn't be a problem if that would happen sometimes. But that has become the rule, not the exception