Mean Mr. Mustard’s List of Original (I believe) Cinematic Sure Things

[commasense]

Any woman who vomits or is nauseated is pregnant.

In a period piece, anyone who coughs more than once will die of consumption.

@Beckdawrek

Oh and my favorite a thousand bullets will only kill or wound 2 good guys.
One, poorly aimed under stress, bullet will mortally wound the bad guys in the last minutes of the movie.

Roger Ebert dubbed this the “Law of Evil Marksmanship.”