The person who notices a missing detail should not be blamed for making the timeline more honest.

The trouble existed before anyone mentioned it. Noticing a missing piece does not add delay to a plan, it moves the delay from the future into the present, where something can still be done about it. When the person who spoke up takes the weight of the bad news, everyone learns that a comfortable schedule is worth more than an accurate one.

If someone brings you an inconvenient detail this week, thank them out loud before you touch the timeline. Separate your feeling about the news from your response to the messenger. Adjust the plan to the truth and let people see that it was safe to speak.