[lotsofpulp]

> you literally cannot discern anything of value from a one-time viewing of them.

The goal is not to discern anything about a particular person from a one-time viewing of them, the goal is to discern something about a person a sufficiently high percentage of the time. Hence the evolutionary utility of using prior probabilities.

As history, and probably many people’s personal experiences, have shown, this trait also has drawbacks.