Idempotency - famously complex. No one has ever successfully implemented it, great point.
If you don't think idempotency can be complex then you haven't really worked on serious distributed computing problems.
If you don't think your analogy is a miss then you haven't really read any serious literature.
Hey here's a solution to the halting problem – always assume yes, and then figure out the edge cases. How do you do that? Well that's on you, I did my job.