This should not happen
One of my favorite things to read in exception messages or logs is this sentence:
"This should not happen!"
Why, you say? Because it's enduring proof that programmers overestimate their ability to understand valid program states.
But we programmers seem unable to stop falling for this trap. I'm guilty of doing this myself, on many occasions, and I always have the same thought: This state is not possible, and the message should say so, because if this happens some other part of the program (possibly not written by me) is breaking an invariant.
My most recent observation of this is a recently added message in the Linux kernel:
[ti. aug. 20 17:47:55 2024] Unpatched return thunk in use. This should not happen! [ti. aug. 20 17:47:55 2024] WARNING: CPU: 1 PID: 983 at arch/x86/kernel/cpu/bugs.c:3023 __warn_thunk+0x2a/0x40
But it still did! It always does. And it's been known for a long time.