9. Mystery Ambulance - Die Hard
Okay, so this plot hole wasn't solved in the conventional sense, but director John McTiernan has laid it the rest with the hope that the audience can understand how it was made, in hopes that audiences will see it as not too big a deal.
Die Hard is one of the best action flicks ever made and a bonafide classic, with great characters and brilliant action sequences. But there's one thing that has come in fans' attention since its release in 1988; where did the ambulance at the end of the film come from?
One of the terrorists ventures down to the car park of Nakatomi Plaza to retrieve the vehicle, which is being stored in a bigger van; the same van the terrorists arrived in at the beginning of the film. The only problem is, when the terrorists arrive during the film's first act and leave the van, there is no ambulance inside of it.
McTiernan has gone on record over the years to apologise for the blunder, and said it was simply because the ending of the film hadn't been finalised when they filmed the terrorist's entrance. It does beg the question, though: why not go back and fix the error? Well that one's simple, too: McTiernan simply didn't notice the mistake until the film was out for the world to see.
It's a shame really, that such a mistake got through, since Die Hard is so good, but it's a perfect example of how not everything can be perfect.