Nowadays game secrets don't remain elusive for long, especially in new releases. The internet picks apart and analyses games to the most extreme degree, meaning that - most of the time - we're just a Google search away from answers on shortcuts, easter eggs and all manner of small but fun details.
Older titles had the benefit of mystery back in the day, however, especially before the web era or in the early days of dial-up connections and limited websites. For fans the only way to get answers was from other players or magazines; the former sources could be very wrong, just ask gen 1 Pokémon fans looking for Mew.
A fun example doing the rounds on Reddit relates to Super Mario 64. In the Castle Courtyard a statue had garbled text that sparked one of the most famous 'mysteries' of that era; that of 'L is Real 2401'. It all originated from some fuzzy low resolution text, which some interpreted as saying 'Eternal Star', and others as the mysterious 'L is Real' phrase. The following post is another from the Nintendo scene on reddit, which shows the statue's text.
For the L is Real crowd, this was a clue; it set off a great search for Luigi in the iconic game - they were searches that proved fruitless. In a popular post, user 'zehnen' shared an image of an old letter that he found in which a Game Play Counselor at the time responded to a letter he sent to Nintendo of America. The letter simply states that 'L is Real' was put in the game as a joke, not a reference to Luigi being hidden in the game.
Of course, not everyone will take this 1998 letter as gospel; some believe the text does say L is Real 2401, but is actually a reference to the release date of Paper Mario, to which the number is close (if not exact). We'd be more inclined to think the potential reference was a joke rather than referring to a release date 3-4 years away at that time.
The smallest things can drive eagle-eyed gamers crazy; in the end, L was not real in Super Mario 64, but he did appear in Super Mario 64 DS.