Question

what is the meaning of split hairs? we agree on almost all of the plan, so why should we split hairs over this one detail? to make a firm demand to fight over tiny differences

Explanation:

The phrase "split hairs" is an idiom. In the given context, since they agree on almost all of the plan, the idea is not to focus on minor, trivial differences (the "one detail"). "To fight over tiny differences" fits this context as an idiomatic meaning. "To make a firm demand" does not align with the context of having a minor disagreement over a detail.

Answer:

to fight over tiny differences