Important Character, Important Evidence

In mystery fiction (not necessarily crime fiction), the important evidence is found by important characters. It doesn't matter how many people are searching, how inexperienced the main character is at mystery solving, or if they are operating out of their field.

They could be off the case, sent home sick, having a day off, late for work, etc. Someone will throw the evidence out the window of a moving car for it to hit them in the face. No matter what, main characters find the evidence.

This trope is understandably found everywhere in mystery fiction, since main characters are meant to drive the plot, yet most authors do not attempt to explain the continuing good fortune of sleuths, both amateur and professional, finding that one piece of evidence that not only seals the mystery up in a neat little package, but also managed to elude everyone else.

Of course, maybe they wouldn't be main characters if this sort of thing didn't happen to them.

Related to Busman's Holiday

Examples:

Literature

Hercule Poirot
Miss Marple
Harry Potter
Sherlock Holmes
- Au contraire, Holmes tends to take evidence already found and derive new meaning from it.
In Edgar Allan Poe's The Purloined Letter, Detective Dupin finds the titular item because he's the only person clever enough to try to think like the thief does.
Harry Dresden. But then, there's a very good reason he finds most of it, all things considered.
Almost any Amateur Sleuth or Little Old Lady Investigates. If they weren't finding the evidence, the story would be about the person who was.

Television

Scooby Doo
Dexter
- Somewhat justified. In the first season, he seemed to have tremendous luck following the Ice Truck Killer (at one point a victim's head is thrown at his car), only it turned out the ITK specifically wanted Dexter, and only Dexter, to follow the clues. The rest of the time, it's because Dexter is willing to use highly illegal means of gathering evidence, something most cops are generally smart enough to refrain from doing, since any decent attorney can get such evidence thrown out.
CSI

Grissom: Wait a minute... enhance that photograph...

House
Columbo
A Touch of Frost
In Monk and Psych this is justified -- they're the only people in their departments who can find the evidence.