"There's two hard problems in computer science: we only have one joke and it's not funny" which I've seen credited to Phillip Scott Bowden

Which is a reference to the "two hard problems" jokes, the most used is "There are two hard problems in Computer Science: Cache invalidation, naming things, and off-by-one errors"

But there is also "Two hard problems in distributed systems: Exactly-once delivery, guaranteed order of messages, and exactly-once delivery".