"This plane is headed to Dallas. If Dallas isn't your destination, this would be a great time to deplane."
After a decision is taken and the organization is moving forward, it's fun and easy to be the critic, the rogue and the skeptic. Easy because the chances that you will have to actually take responsibility for your alternative view of the future are slim indeed–the plane is already headed somewhere, it can't go both places and you missed (or bungled) your chance to change the decision.
No, the time to speak up is before the decision is made, when not only do you have a chance to change where the organization is going, but you have the responsibility to deliver on your vision.
We don't have time to revisit every decision our organization makes. We merely have the time to do the best we can to execute on what we've already committed to do.
Rooting for your team to fail is as bad as it sounds. Even if you said early and often that this path was a stupid one, that this destination makes no sense–if you're on the plane, if you're in the meeting, if you decided to play the game–then once the journey starts, your job is to get us there, safe and sound.
And then come to the next meeting with a better plan about the next decision.