The strongest concession is one that costs you less than it matters to them.

The best trades exploit differences in valuation rather than splitting the difference. Something that means very little to you, timing, a name on a document, a small piece of flexibility, may be central to them, and giving it costs you almost nothing while buying real goodwill. Finding those asymmetries is most of the skill. It is not generosity; it is efficiency.

Before a negotiation, list what you could concede cheaply and what you cannot. Then look for what they seem to care about disproportionately. The overlap is where the deal usually gets better for both of you.