Fairness becomes complicated because humans are not interchangeable variables.

Any fair rule has to be written in general terms, and people arrive with histories, capacities, and burdens that no general term captures. What looks like an equal division on paper lands unequally the moment it touches actual lives. This is not a flaw to be engineered away; it is the permanent difficulty of applying anything uniform to beings who are not uniform.

When you make a rule for a group, expect it to fit badly somewhere and decide in advance how you will handle that. Naming the likely misfits up front is more honest than pretending the rule is perfect and then quietly granting favors to whoever complains loudest.