I encountered something like the 5-and-10 problem in the art market. If I like a picture of the artist A, and I know that I have a good taste, it is an evidence that artists A is good, so I should buy it. The more good art I found, the better is my taste.
Now repeat it 100 times and you end buying pile of garbage.
Logical counterfactuals are key to Functional Decision Theory and last I heard still an unsolved problem. Unfortunately, I am still rather confused about what exactly we are trying to solve. The only concrete problem I know of in this space is the 5-and-10 problem. But as far as I know, this is solved by writing programs that immediately cause a paradox if they ever discover their output. So presumably there are some unsolved concrete problems that relate to logical counterfactuals?
Edit: I should mention my post on the Cooperation Game as an example. Plus the further work section of this slideshow.