#1 All ventilation ducts are large enough to admit a full grown man with weapons and equipment. (Also, any ventilation duct that the hero crawls into will automatically lead to wherever he needs to go, typically without connecting to any actual air conditioning equipment.)
#3 No matter how much ransom is demanded, the money will always fit into a single briefcase.
#4 It is technologically impossible to construct an explosive device that does not include an LCD timer, and/or flashing red LED lights.
#5 No matter how much of a head start you have or how fast you run, when you stumble the monster will catch you. (This applies even if you are an Olympic runner, and the monster is shambling along like an old man on crutches dragging an anvil.)
#6 Autistic or developmentally challenged children are nearly always savants, who can break military-grade encryption schemes without computer, calculator, or scratch paper.
#7 The bad guy is never dead the first time. In fact, he is rarely dead the second time. (Even if he is utterly destroyed with no possibility of resurrection, a truly determined bad guy can come back from the dead in time for the sequel.)
#8 If you kill the hero’s friends or family, you might get away with it. If you kill the hero’s dog, retribution will be swift and certain.
#9 A detective cannot solve a serious crime until he or she has been removed from the case and suspended from duty. This usually involves surrendering his or her gun and badge.
#10 The missing piece of the map or message always contains the only information that is really needed.
#11 The hero’s wounds may occasionally start bleeding again to remind us that they are serious, but they will never become infected or require significant medical attention. (On the rare occasion that the hero is admitted to the hospital, when he regains consciousness, he will remove his own IV lines and leave the critical ward to go after the bad guy.)
#12 When vehicles collide, there is a 73.9% chance that they will erupt into fiery explosions.
#13 If you think really hard, you can figure out the bad guy’s computer password in 2 or 3 attempts.
#14 Whenever scientists attempt to cure disease by modifying the human genome, the result will always be a super villain, or an army of zombies.
#15 If the hero needs to learn about an event that occurred a long time ago, he will invariably encounter someone who kept a scrapbook of photos and relevant press clippings.
#16 When a woman takes a bath, the bubbles will strategically position themselves to cover her nakedness. (Exception: If the woman takes a shower and her nakedness is revealed, she will probably not survive until the end credits.)
#17 All serial killers read Blake, Dante, Milton, and the creepier parts of the Old Testament.
#18 Complex electronics are never protected by circuit breakers, surge suppressors, battery backup power, or fire suppression systems. As a result, mainframe computers can be relied upon to explode dramatically when any overload condition exists.
#19 A bite from a radioactive insect or arachnid can give you miraculous powers.
#20 If a crazy old woman utters a prophesy, it will always come to pass. (This is especially true if the old woman is blind, has a severe cataract over one eye, or if she speaks in unknown tongues.)