A good agreement leaves fewer reasons for either side to resent keeping it.

An agreement someone regrets is not finished, whatever the paperwork says. Resentment shows up later as delays, minimum effort, disputes over interpretation, and a reluctance to do the thing again. A deal where both sides feel reasonably treated costs a little more upfront and saves considerably more over the life of it. Durability is part of what you are negotiating for.

Before closing, ask whether the other side will feel decent about this in six months. If the answer is no, adjust something, even slightly. What you give up there is usually less than what a resentful counterparty costs.