If you are a player purchasing the DUNGEONS and DRAGONS rules in order to improve your situation in an existing campaign, you will find that there is a great advantage in knowing what is herein. If your referee has made changes in the rules and/or tables, simply note them in pencil (for who knows when some flux of the cosmos will make things shift once again!), and keep the rules nearby as you play. A quick check of some rule or table may bring hidden treasure or save your game "life".
That's page four, in the introduction of Men and Magic, volume one of the original Dungeons and Dragons box set. I assume those are Gygax's words, but maybe not.
Players should not have the rules hidden from them, and should be able to use them as needed to their character's in-game benefit during play.
It's in print, right there at the beginning. Of everything.