When the plan is clearly heading off a cliff, somebody has to be first to step out of the car.

Groups can see a problem collectively and still keep going, because everyone assumes the others know something they do not. That is how plainly bad plans continue all the way to the end. Breaking it takes one person willing to be the visible objector, which is uncomfortable and briefly makes you the difficult one. It also tends to release everybody else who was thinking the same thing.

If you can see something going wrong, say it once, early, and say it clearly rather than hinting. Name what you think happens next and ask directly whether anyone else sees it. If they overrule you, you have still done your part.