Movie villains, even the ones portrayed as master criminal geniuses, usually spend the movie making incredibly stupid mistakes (accidental or otherwise). So you can almost make a game out of it: The second time you watch any movie involving a supposed criminal mastermind, just imagine how his plan would have gone had the hero not showed up at all.
Because more often than not, you'll realize that his genius scheme would have fallen apart all on its own. What do we mean? Well...
6Die Hard -- Hans Gruber's Escape Plan is Terribly Inadequate
Hans Gruber and his gang of sweater-wearing European dance models lay siege to Nakatomi Plaza, posing as terrorists to conceal their true purpose, which is to steal $640 million in bearer bonds from the building's vault. Once the vault is cracked, Hans plans to send all of the hostages to the roof and blow them up, anticipating that the resulting pile of bodies will be too dense for the authorities to discover that his own corpse isn't among them.
Then, Hans and his gang intend to load the bearer bonds into a fake ambulance, blending into the chaos of emergency vehicles and allowing them to escape undetected.
"I almost brought a school bus, but what idiot would try to flee a robbery in one of those?"
But wait a second ...
Every single step of Hans' escape plan is so terribly flawed that, had Bruce Willis not kicked him through a 40th story window, he and his henchmen would have been arrested before their ambulance even made it to the first stoplight.
First of all, Hans begins the evening with 13 henchmen. Take another look at their escape van:
"Some lap sitting will be necessary."
How the hell is he planning on fitting 13 grown men in that thing? Let alone the stacks of bearer bonds they came to collect, which, we are shown, require several duffel bags and a hand cart to transport:
"Nobody ate this morning, right?"
There's also the matter of actually exiting the parking garage. We see Hans and his men lock the gates, which is what traps Argyle the limo driver inside for the entire movie. Argyle only gets out because he finally decides to crash his limo into one of the exits:
It took him two hours to figure this out.
When the FBI shows up, they cut the power to the building, meaning the electronic gates in the garage are now frozen in place. Hans would have to plow his ambulance through the bars just like Argyle in order to leave, and we're willing to bet one of the 100 or so cops on the scene would notice something like that.
Even if he manages to get out of the building, Hans is far from home free. The whole point of the terrorist song and dance he feeds the FBI is to disguise the fact that he's really just a bank robber. According to his plan, blowing up the roof will lead everyone to believe that he and his extremist buddies detonated themselves and their hostages, because that's the kind of silly bullshit that terrorists do. However, the bomb doesn't destroy the vault, and Hans never intended it to. Meaning he purposely left a giant, empty safe hanging open for the authorities to find.
"... just leave a note saying it was like that when we got here."
It won't take them too long to identify the charred bodies, particularly when they already know exactly how many hostages were in the building. When the FBI realizes their count is short a few terrorists and about half-a-billion dollars, they're going to know that Hans took that fucking money. At best, he's bought himself an extra week, and then Interpol is going to burst into his Majorcan hotel room and drag him out through the lobby in his bathrobe.