"Never Split the Difference" is also the name of an outstanding book by Chris Voss, the former head of FBI hostage negotiation. For shorthand, Voss refers to all biz school rational-actor negotiation theory (as espoused by the parent post, for example) as “splitting the difference.”

He holds that such theory is useful to know in general, but that real-world negotiations are carried out by emotional, irrational humans. As a result, these rational theories often break down in the face of hubris, anger, fear, love, shame, etc, and as such, relying solely on these theories will not get you the results you want. Thus, you should "never split the difference."

Instead, he then goes on to suggest a whole variety of ways one can achieve better negotiation results, starting with the most obvious: really, truly listening to the needs of the other. The book is fascinating. Highly recommended.

How would a desperate car salesman use that phrase?