IT's magic.

Our approach in this paper is not only constructive, but we consider it to be procedural as well. In the context of fair division, we view a procedure as featuring the following characteristics: it is intuitive, meaning that each step must be easy to understand; it is plausible, meaning that each step must be simple to argue; and it is manageable, meaning that each step must be straightforward to compute. We see these subjective criteria as relevant for the practical implementation of a fair-division outcome, in particular when parties in real life prefer to establish fairness by themselves, rather than trust the ‘‘magic’’ of a computer algorithm.

Claus-Jochen Haake, Matthias G. Raith, and Francis Edward Su. Bidding for envy-freeness: a procedural approach to n-player fair-division problems.
In: Social Choice and Welfare, 19(4):723–749, 2002.