This idea is the basis of integrative negotiation. Integrative negotiations are negotiations in which both sides can gain. They are not zero-sum affairs. Therefore, when negotiators can generate alternatives that allow for mutual gain, they are creating integrative negotiations in which win-win solutions are possible.
In a distributive negotiation (or one that the two sides think is distributive), any gain on one side must be accompanied by loss on the other side. The classic example of this is a case like last summer's NBA labor talks. There, owners wanted a lower percentage of revenue to be paid out to players while the players wanted more. If the two sides in this negotiation could have found alternatives for mutual gain, things would have gone better. For example, they might have agreed to keep the percentage of revenues where it already was while finding new ways to increase the amount of revenue flowing in. The more of these mutually beneficial solutions that can be found, the better the chance of having a win-win solution.