Stranger Safety

The tendency of fictional works to assume that characters can talk to, share a room with, or travel with complete strangers without doing a background check or even a basic spot check - and despite this, nothing bad will ever happen.

In stories where this trope applies, it's usually a near unheard of and an unspeakable crime to actually lull someone into a sense of security and rob them blind. Doing so in such a story is sure to send the character straight over the Moral Event Horizon and into Complete Monster territory. Why else would it be pounded into most of the children of Real Life that talking to complete strangers is usually bad?

A Justified Trope, as in ancient Greece, accepting aid from and giving aid to complete strangers was shown to be a virtuous characteristic. Even in relatively recent times and stories it was not improbable for these sorts of events to occur; strife at them is likely to be due to Values Dissonance.

When this trope is in play, Walking the Earth may become easier.

Anime and Manga

In an episode of Cardcaptor Sakura, a strange old man befriends ten-year-old Sakura. It turns out to be her great grandfather, but she didn't know it at the time and went off with what could very well have been a creep showing unnatural interest in her. Moral Guardians were so very unamused.

Literature

In Moby Dick, Ishmael isn't put off by having to share a bed with a complete stranger, until he discovers the stranger in question is a Wild Samoan. An example of Values Dissonance, as that was how inns and guest houses worked back then. A bed to yourself was very, very expensive.
Ayla and Jondoloar from the Earth's Children series are constantly meeting new people, who are (almost) always helpful and friendly.
In Lonely Werewolf Girl Moonglow and Daniel take in werewolf Kalix no questions asked, even when they know she is a werewolf with self destructive tendencies, no social skills, and hunted by, well pretty much everyone.

Live Action TV

Happens all the time in Highway to Heaven. After meeting Jonathan (the angel) and Mark (his sidekick), people rarely suspect any danger of any kind from these two. In one rare instance (in the episode Monster) where a boy does distrust strangers, the episode is about tolerance of those who are diffent. The boy turns out to be a liar who can't be trusted. Within a day or two of knowing someone Mark and Jonathan will be granted full access to loved ones and personal property beyond what a normal person would trust his own spouse or children to do. In some episodes, Jonathan has convinced near complete strangers to:
- Let him live in their houses.
- Cash in their entire life savings - and hand the cash over to him - to bet on a horse race!
- Take out a mortgage on their homes - and hand it over to him - to invest in the stock market.
- Take his word for it when a loved-one is sick or missing. Most people are satisfied with, "I think I know where to find him," or "You're just going to have to trust me." Never mind that Johnathan is a drifter with no ID and a new job in every episode.

Mythology

Played straight in The Odyssey, where many characters take care of main hero Odysseus.

Video Games

Both Pokémon Mystery Dungeon games start in this manner. The first game is particularly jarring, as you, a complete stranger, are tasked to rescue a baby Caterpie.
- Subverted in the second game, where a Drowzee kidnaps Azumarill, the game's resident Cute Shotaro Boy.
In The Legend of Zelda, many fans have commented on Link's ability to just walk into anyplace. Few NPCs will care that much about you breaking pots and taking the goodies inside, or just walking around. Bedrooms aren't off-limits. Some places can only be entered during the day, though.

Western Animation

The Simpsons Musical Episode "Oh, Streetcar" featured a song which had a message of "A stranger's just a friend you haven't met yet!" This is a parody of the same line's darkly ironic use in the original play.

Real Life

An aspect of this fits into the general aspect of hitchhiking and picking up hitchhikers. Hitchhiking was once considered a perfectly reasonable way for young people to travel, and it was considered bad hospitality to not pick up stranded travelers along the way. Now, the general feeling is to lock one's doors; both the hitchhikers and the drivers expect the other to be scumbags who will take advantage of them, attack them, or take advantage of them and then attack them.
- Many an older person will tell you that you didn't have to be as careful a few decades ago as you do now, but it's hard to know if that's the Nostalgia Filter talking if you weren't there.