It's a well-known principle in screenwriting that the audience will accept any coincidence - no matter how outlandish - as long as it has a negative effect on the protagonist.
In other words, if a movie hero has an immunity to snake poison, and then the treasure just happens to be guarded by snakes, the audience will feel the scene is unsatisfying, too convenient, mere coincidence and contrived.
But if the treasure is guarded by snakes, which happen to be the hero's worst fear in the entire world, it's no more or less coincidental than before, but the audience reaction is the exact opposite - they find the situation to be dramatic, exciting and fulfilling.
Now let's apply it to advertising.
Lucky, the former More Th>n insurance spokesdog, starred in a series of adventures in which, by coincidence, a chain of potentially disastrous events caused no damage. Guess what? Those ads weren't good. They felt cheesy. Whereas in Levi's "drugstore", my favourite ad of all time, there is a similar coincidence - the pharmacist who sells our hero his condoms just happens to be the dad of the girl he's taking out that night. And it's thrilling.
So that's the tip. When you use coincidence, make sure it's causing a problem and not a solution.Your ads will seem dramatic and not contrived.