Why splitting the difference rewards the extreme opener

Splitting the difference is the most respectable move in bargaining. It ends arguments, it looks even-handed and it requires no information about value. It also makes the outcome a function of two numbers chosen by the parties themselves, one of which may have been chosen for precisely this reason.

What everyone sees

The midpoint reads as neutrality. Both sides gave up the same distance, so nobody exploited anybody, and the settlement can be defended to a committee without further justification. Where the two openings came from is treated as prologue rather than as evidence.

What is actually happening

Equal concession in distance is not equal concession in value. If one side opens near its true reservation point and the other opens far beyond its own, the midpoint falls inside the second side’s surplus. Anchoring research adds a second effect: first offers pull the eventual settlement directly, so the extreme opener collects twice, once through the anchor and once through the arithmetic.

Why it stays hidden

The rule survives because it is procedurally beautiful. It is symmetric, it is easy to explain, and it spares both negotiators the argument about worth. That makes it attractive to the weaker side as well, since accepting a mechanical rule feels safer than defending a valuation — and the safety is real, which is why the cost is so rarely counted.