Someone (I had thought it was MJD, but uncle GOOG is not pulling it up on his blog) once told a story about how software estimation was a bit like transfinite recursion on ordinal numbers: sometimes you have an estimate in ℕ, and it's possible to say "I'll be done in 5 days, give or take", but sometimes your estimate is above omega, and the best you can do is tell someone who asks "Right now, I don't know how long it'll take, but come back in 5 days (give or take) and then I can tell you".<p>(and it wasn't JDH, either: closest I get there is <a href="https://jdh.hamkins.org/transfinite-nim/" rel="nofollow">https://jdh.hamkins.org/transfinite-nim/</a> )