The TV Tropes website defines fridge brilliance as a circumstance where your reaction to something you read, watch or listen to is one of confusion and annoyance, but which, at some unspecified point later (proverbially, when you are just going about your life, opening a fridge to get out some food or drink) makes you go "A-ha! NOW I get it!"
Hans Perk posted the animator drafts for the cartoon "Donald's Lucky Day" in August 2006. The following month, Mark Mayerson posted a mosaic of the short, a critique of the story and some thoughts on the animators. It's the critique of the story which I'm mainly interested here, I just provided the other links for background info.
Some of Mayerson's critiisms are deserved: for example, the cat just disappears after the bomb goes off, and the fish are eaten by a smarm of anonymous cats rather than the one who's been appearing throughout the cartoon, which isn't a very satisfying ending. (Actually, it suggests the poor cat was blown up or drowned, which probably wasn't their intention) It would have been better if it had ended with the "hero" cat chowing down on fish, and Donald doing one of his end-of-cartoon "aw, shucks" type chuckles.
However, another of his comments is that Donald "would have been luckier if he lost the package immediately and saved himself a lot of effort." However, this would be impossible, because... it was still Friday 13th! The bomb is supposed to go off at 12 o'clock, right? So, up until that happens, it's Friday 13th and Donald is having an unlucky day. After the bomb goes off, it's now Saturday 14th. Donald exclaims "This is my lucky day!" meaning the new day that's just started. In fact, in the opening scene with the gangsters, they refer to the bomb as a "valentine", so they're thinking of it as going off at the start of the 14th (February, that is) as well.
OK, I don't know if that's what the intention of the writers/animators was. If it was, I guess the main problem is that they didn't make it clear enough. So, here's my revised ending:
Donald gets covered in fish. He hears on the radio something like: "When you hear the sound of the tone, the time will be 12 o'clock, midnight. That's the end of Friday 13th. Did you all make it?" Donald, overjoyed: "Oh boy! This is my lucky day!" Then the cat emerges out of his hat, gobbles down a fish, and rubs against Donald's face. Donald chuckles awkwardly. End.