Philosophy : Diplomacy
The core of every negotiation is the position of strength. Strength is a multi-dimensional vector, like force in physics. Which of the axes of the strength vector matters, depends on the desires of the opponent. For example, a superiority in military force does not matter to an Islamist that wears a bomb belt and considers its death to be a divine and good thing. Lack of strength at the axis that matters to the opponent can not be compensated by superiority at some other axis.
Parties can trade to compensate each-other's lack of strengths. Trade is an unreliable solution, but it can help out probabilistically. The reason, why it is irrelevant, what opponents think is that opponents may switch the axes of strength that matter to them. The switch of axes by the opponent may move the proponent from the position of strength to a position of weakness. That's why the various spying for finding out opponent's opinions wastes the proponent's negotiators' time, because they have to spend time reading, getting acquainted with, the spying reports. A reliable solution is based on a Graph of Failures. Anything less than the strategy based on the Graph of Failures is a shoddy compromise, essentially a job not done.