That's always been a D&D cliche that I've found slightly mystifying. If the player, who plays D&D as a hobby, know that a mummy is vulnerable to fire, why wouldn't the character, whose life depends on knowing how to fight monsters?
It's a cliché of the "thespian" clique, those who somehow mistake a *g*a*m*e* for
Masterpiece Theatre.
It was clearly no expectation in 1974, when the very first published rule-book advised
A quick check of some rule or table may bring hidden treasure or save your game "life".
However, by 1976 (Supplement III) it was clear that
somewhere along the line, D&D lost some of its flavor, and began to become predictable. ... When all the players had all the rules in front of them, it became next to impossible to beguile them into danger or mischief.
And so, Gygax called the Advanced D&D
Dungeon Masters Guide "the exclusive precinct of the DM".
Peeping players there will undoubtedly be, but they are simply lessening their own enjoyment of the game by taking away the sense of wonder that otherwise arises from a game which has rules hidden from participants.
I'm not sure whether the DMG mentions it, or what rule applied in the tournaments at GenCon and Origins, but as I recall it was customary for players not to have access to the
Monster Manual during an actual session of play.
Real experience and skill gained in play would in due course distinguish old hands from novices.
DMG said:
Other experienced players will have no characters, but they will have useful knowledge of the game which puts them apart from true novices. ... Experienced players without existing characters should generally be brought into the campaign at a level roughly equal to the average of that of the other player characters ... After all, they are not missing out on anything, as they have already played beginning character roles elsewhere ...
On the other hand,
The inexperienced player should be allowed the joy of going on a dungeon adventure as a neophyte. You will recall how much fun it was when you didn't really know what was going on or which monster was which or how to do anything but loved every second of it! Throwing a green player into a group of veteran AD&Ders destroys all hope of that, for the inexperienced player will be suppressed or repressed or both.
The way to surprise experienced players is with
new monsters and magic, and more cunning tricks and traps. Someone who has played for years might sometimes choose to make a bad move because it's "in character" -- but trying to
push people into that position is obnoxious.