You have several hundred school kids, who choose their elective subjects, two or three of them (4 hours per week at the most in total), for the entire next school year.
It is possible for the school to have 25 of those subjects, chosen among 36 possibilities. So they ask kids, what they wish to learn. Each student makes his or hers top 5 list.
The most wanted was German language, the least demanded was Chinese language. 30 students wanted German language as their number one choice and 10 students wanted Chinese language as their number one choice.
Fortunately, exactly 25 subjects were even mentioned by students. The only problem is, that the group of 30 students is too big and should be split into two smaller, for the law and safety reasons. But then, one other group has to be canceled. Those 10 who wanted Chinese should accept some secondary choice like music, sports, experimental chemistry and so on. There will be no Chinese course next year.
Or, 2 of those 30 who wanted German language should accept some less desired choice like painting or philosophy and then there will be room for the Chinese language course.
This is a frequent real life dilemma I saw many times in the last 10 years. In reality it’s more complicated than that, but essentially the same.
It is easy to say – well kids, there won’t be no Chinese language course next year, due to the lack of interest and our limitations. But it is harder to say, there will be no German language just for you 2, despite the fact that other 28 will have it.
What is the right thing to do?
protokol2020 
I think it’s clearly better that two kids don’t get to do their favourite subject than that ten kids don’t get to do theirs. The only difficulty is that it will feel unfair to the two who are chosen, whereas excluding the ten students who preferred Chinese would seem less arbitrary. The solution is to (a) never mention to the students that you had other options and (b) announce in advance that German is oversubscribed, wait a bit, and then pick two kids at random. That way the kids know that you made a fair decision under unavoidable circumstances.
I most certainly agree with what you said.
But some principals say that this position is indefensible in practice when the kid’s parents come and demand the same treatment for their kid, as their neighbour’s kid has been treated.
It’s about half/half division on this matter, roughly. From my anecdotal observations.