If the deal only works when nothing goes wrong, it’s not a deal. It’s a bet.

Any arrangement that needs every part to go right is not really an arrangement, because things reliably go partly wrong. Hours get cut, a car breaks, somebody drops out, money turns up late. A plan with no slack in it is a prediction wearing an agreement’s clothes, and the question is never whether it works perfectly but what happens when one piece slips.

Name the two things most likely to go sideways, then ask who carries it when they do. If the answer is you and you could not absorb it, you have your answer. Build the margin in before you need it.