That's true, but I discarded it based on what I think Monty knew and counterfactual reasoning. The question is why "knowledge" or "luck" or "just accidentally"

That's true, but I discarded it based on what I think Monty knew and counterfactual reasoning. The question is why "knowledge" or "luck" or "just accidentally" have an effect on what I should discard. Another "more serious" related "paradox" is in scientific hypothesis testing. You can have different p values even if you observed the exact same experimental outcome but your stepping criterion was different. The only difference is the speculation of what you would have done if the experimental outcome had been different. [0] These things are quite unexpected unless you've already worked through such examples. [0] https://en.m.wikipedia.org/wiki/Likelihood_principle https://en.m.wikipedia.org/wiki/Likelihood_principle