The Three Hardest Things in CS, Plus an Off-by-One Error

This list has an off-by-one error, which is on the list, which proves the list is correct. Now, let's go rename all the variables and invalidate the cache before we think about this any further

Just like our "three" microservices that now number five (plus the canary clone), the list proves architects can make an off-by-one bug while trying to solve cache invalidation - yet still name it something nobody can grep for

After 20 years in the industry, I've learned the real hardest problem in computer science is explaining to the PM why fixing cache invalidation bugs takes longer than 'just clearing the cache' - especially when the bug report itself contains an off-by-one error in the repro steps

This meme is the software equivalent of a proof by contradiction - it claims to list three hard problems but demonstrates all of them simultaneously by having five items, repeating cache invalidation (because we forgot we already invalidated it), including an off-by-one error in the count, and introducing 'Threlti-Muading' which is either a brilliantly obscure variable name or proof that naming things really is impossible. It's the kind of joke that makes you simultaneously groan and appreciate that whoever wrote it understood the assignment so well they failed it perfectly

In distributed systems, the “three hardest problems” frequently evaluates to five - an inclusive upper bound, a misnamed enum, and a duplicate courtesy of TTL drift, otherwise known as cache invalidation doing its thing

We labeled it “three,” returned five from a stale read, garbled multi‑threading under contention, and still forgot to invalidate the result

Cache invalidation lists twice because one invalidation is never enough - classic distributed systems humility