I don't understand checks, but isn't it just paper that allows transfer of money to the person the check is addressed?

If so, what does it matter that someone else cashed it? Such transaction is unauthorized, it's a matter between the bank and the thief, and doesn't concern Mr. Handy.

What concerns Mr. Handy is Paychex refusing to honor the check. Presumably they are claiming he authorized transfer of money to a person that neither Paychex or Mr. Handy can identify.

Probably PayChex has a weak claim there :)

Again, I don't fully understand checks -- but my impression is that because a check is (often) addressed to a person, they are actually pretty safe. I'm assuming fraud is always the responsibility of the bank that failed to verify addressed person. Hence, why cashing a 100k check probably isn't easy to do -- stealing to check is probably the easy part. Cashing it without getting caught is the impressive part.

That said: In practice, I'd never want to use a check.

Yeah it should be the fault of the bank that didn't check things before cashing it.

There are various attempts to phase checks out, and switch to FedNow and RTP instant payment rails. Unfortunately, there is no legislation requiring a deadline to phase out paper instruments such as checks. Call your Congressional rep. The infra already exists, anyone dragging their feet has limited incentive to hurry up.