They stumble across a ghost town inhabited by a rascally gold prospector.
You stumble across some great ones and you say, "This is fantastic, why doesn't somebody just make a list of all the great pieces so I don't have to look at the rest.
Say you stumble across a news story you like. You "Digg" it, by clicking a link at the end of the story.
And part of that is absolutely putting games in places that you wouldn't expect them, such as a record shop, such as a shopping precinct, such as a library to allow people to stumble across them.
Thus, if you stumble across old course material with similar-looking problems, please try not to look at their solutions, but rather work the problem (s) yourself.
As with dislocating functions, you want to make these types of functions more difficult for your users to stumble across.