The case in three lines. Two days after joining the games club, Ellis's homemade game tops the club's rating site on two votes, above a game sixty people love. The committee wants to hide new games until they have twenty ratings; Sol points out that a hidden game can never earn them. Priya, Dunna and Vera work out a fairer rule: start every game at the middle and let votes move it in proportion to how many there are. The sponsor asks Tara how the list should work, and the case stops there.

One question to ask. "What did Tara say?" Then: "Is a formula people can't check fairer than a simple one that's wrong?" A good answer takes Ms. Varga's worry about trust seriously.

One thing to do at the table. Think of a time you formed an opinion of someone or something from very little: a first meeting, one review, one bad day. How many more "votes" would it have taken to change your mind? How many did you actually wait for?

The grown-up layer. The case is about priors. In Bayesian reasoning you begin with a starting belief and update it as evidence arrives, giving evidence weight in proportion to how much of it there is. Rating sites use the same idea, a Bayesian average, to stop a handful of scores topping a list. The case also offers the idea as a way to meet new people: start in the middle, and let a lot of ordinary evidence move you more than a few loud moments.

The case leaves Tara's sentence blank on purpose. Ask for it before you offer yours.