Nagotiantions are not a zero sum game
Deals do not have to feel fair.
The idea that deals need to be fair is based of the idea of that negotiations are a 0 sum game. If I'm getting more than half then the other party is getting less than half and the Golden_Rule fallacy
Fairness is subjective.
It doesn't concern you if a deal is fair to your perspective. A deal does not have to be fair it just has be that each side doesn't feel taken advantage of(after they become fully aware of the situation).
Suppose there are two children, one at the preoperational stage and the other at the concrete operational stage, and there are three 8 oz. cans of soda and two 16 oz. can of soda that need to be divided between them.
If you insist that the deal be fair the best you can do is give each child a 8 oz. can and 1 16 oz. can. But you can do a deal where both parties believe that they got a better deal than the other. Give the preoperational child the three 8 oz. cans and the concrete operational child the two 16 oz. then both child have gotten a better deal than the other. The preoperational child got one more can of soda than the other child. The concrete operation child got 8 more oz. of soda than the other child.