In SAFe and Scrum at every PI planning and at every sprint planning I always ask the team about there commitment to the delivery, I ask them if they are willing to make a promise to the Sponsors, Product Manager and the Product Owner, and most importantly of all promise to each other that they will do everything within our power to get this done. Its important they think about this decision, one of the many benefits of the fist of 5 (widely used in in SAFe) is a give them a pause for thought. What the vote, assuming its a free vote will tell you what they really think. Tell you what the probability of success is.