Depends. I believe in the notion that the condition should be phrased the way the statement it modifies behaves.

F.ex, if I am using die to catch an unexpected case, then the condition I use would also be the unexpected case - f.ex, if I expect things to work correctly almost always, I would write "die if no success" or "die if failure". Contrast with "die unless success" or "die unless no failure" - they seem to suggest that most of the time, we'll have failed at this point.

Conversely, if I expect statement being executed to be the norm, then I'd use the expected case as the condition: "increment counter if another entry is to be processed", or "increment counter unless this was the last entry".

Makeshifts last the longest.