[azalex]

It does happen, quite often, to be honest. The single most important thing in this case is to understand why it happened. A typical example is when we come up with a design proposal that I think is a good one, but turns out to be that the estimated cost of building and running it outweighs the projected revenue the product will generate. Another example would be when I want to have a particular design implemented by an engineering team but they don't have enough capacity (people, time, etc) to deliver it the way it was intended. There have been cases when it was all about politics (sadly, I must add, but it does happen), i.e. someone in higher places of power want to push their own agenda and you get overruled.

These are cases when the previously mentioned 'professional negotiator' role gets really important. These are the cases when you need to go to the people involved and try to understand their priorities and their constraints. Once you have the information necessary, most of the times you'll be able to come up with an alternative solution that is acceptable for everyone. Sometimes you can convince others to give way, sometimes you'll need to.

And then there are times when you just can't do anything because, for example, you get overruled by an overzealous CTO. In these cases, as sho_hn also pointed out, the best you can do is to make them understand the implications and brace yourself for damage control, because the fallout is going to be on you anyway :)