Understand the underlying and ancillary motivations of the other side. Oftentimes there are conflating or conflicting interests at hand. As much as possible, you need to understand the total “motivational picture” of your counterparty. For example, at our firm we have been in negotiations where we ultimately learned that what appeared to be irrational negotiating by the other side was driven by how they were compensated for the deal. Where possible, uncover if those negotiating for other side have any personal remuneration at stake, and how that changes with different outcomes – it will drive behavior.