The following is text from the "Dungeons & Dragons Dungeons Master's Guide" first edition, by Gary Gygax (copyright 1979). This is selected text which reveals the authors' view of what roleplaying is and the responsibilities of GM and players.
"CONDUCTING THE GAME", page 110
In many situations it is correct and fun to have the players dice such things as melee hits or saving throws. However, it is your right to control the dice at any time and to roll dice for the players. You might wish to do this to keep them from knowing some specific fact. You also might with to give them an edge in finding a particular clue, e.g. a secret door that leads to a complex of monsters and treasures that will be especially entertaining. You do have every right to overrule the dice at any time if there is a particular course of events that you would like to have occur. In making such a decision you should never seriously harm the party or a non-player character with your actions. "ALWAYS GIVE A MONSTER AN EVEN BREAK!"
Examples of dice rolls which shoudl always be made secretly are: listening, hiding in shadows, detecting traps, moving silently, finding secret doors, monster saving throws, and attacks made upon the party without their possible knowledge.
There will be times in which the rules do not cover a specific action that a player will attempt. In such situations, instead of being forced to make a decision, take the option to allow the dice to control the situation. This can be done by assigning a reasonable probability to an event and then letting the player dice to see if he or she can make that percentage. You can weigh the dice in any way so as to give the adventage to either the player or the non-player character, whichever seems more correct and logical to you while being fair to both sides.
Now and then a player will die through no fault of his own. He or she will have done everything correctly, taken every reasonable precaution, but still the freakish roll of the dice will kill the character. In the long run you should let such things pass as the players will kill more than one opponent with their own freakish rolls at some later time. Yet you do have the right to arbitrate the situation. You can rule that the player, instead of dying, is knocked unconscious, loses a limb, is blinded in one yee or invoke any reasonably severe penalty that still takes into account what the monster has done. It is very demoralizing to the players to lose a cared-for player character when they have played well. When they have done something stupid or have not taken precautions, then let the dice fall where they may! Again, if you have available ample means of raising characters from the dead, even death is not too severe; remember, however, the constitution-based limit to resurrections. yet one die roll that you should NEVER tamper with is the SYSTEM SHOCK ROLL to be raised from the dead. If a character fails that roll, which he or she should make him or herself, he or she is FOREVER DEAD. There MUST be some final death or immortality will take over and again the game will become boring because the player characters will have 9+ lives each.
Some players will find more enjoyment in spoiling a game than in playing it, and this ruins the fun for the rest of the participants, so it must be prevented. Those who enjoy being loud and argumentative, those who pout or act in a childish manner when things go against them, those who use the books as a defense when you rule them out of line should be excluded from the campaign. Simply put, ask them to leave, or do not invite them to participate again.
Peer pressure is another means which can be used to control players who are not totally obnoxious and who you deem worth saving. These types typically attempt to give orders and instructions even when their characters are not present, tell other characters what to do even though the character role they have has nothing to do with that of the one being instructed, or continually attempt actions or activities their characters would have no knowledge of. When any such proposals or suggestions or orders are made, simply inform the group that that is no longer possible under any circumstances because of the player in question. The group will then act to silence him or her and control undesirable outbursts. The other players will most certainly let such individuals know about undesireable activity when it begins to affect their characters and their enjoyment of the game.
Strong steps short of expulsion can be an extra random monster die, obviously rolled, the attack of an ethereal mummy (which always strikes by surprise, naturally), points of damage from "blue bolts from the heavens" striking the offender's head, or the permanent loss of a point of charisma (appropriately) form the character belonging to the offender. If these have to be enacted regularly, then they ar enot effective and stronger measures must be taken. Again, the ultimate answer to such a problem is simply to exclude the disruptive person from further gatherings.
"CONDUCTING THE GAME", page 112
While it might seem unlikely to those who have not been involved in fantasy adventure gaming for an extended period of time, after the flush of excitement wears off -- perhaps a few months or a year, depending on the intensity of play -- some participants will become bored and move to other gaming forms, returning to your campaign only occaisionally. Shortly thereafter even your most dedicated players will occaisionally find that dungeon levels and wilderness castles grow stale, regardless of subtle differences and unusual challenges. It is possible, however, for you to devise a campaign which will have a very minimal amount of participant attrition and enthusiast ennui, and it is not particularly difficult to do so.
As has been mentioned already, the game must be neither too difficult to survive nor so easy as to offer little excitement or challenge. There must always be something desirable to gain, something important to lose, and the chance of having either happen. Furthermore, there must be some purpose to it all. There must be some backdrop against which adventures are carried out, and no matter how tenuous the strands, some web which connects the evil and good, the opposing powers, the rival states and various peoples. This need not be evident at first, but as play continues, hints should be given to the players, and their characters should become involved in the interaction and struggle between these vaster entities. Thus, characters begin as less than pawns, but as they progress in expertise, each eventually realizes that he or she is a meaningful, if lowly, piece in the cosmic game being conducted. When this occurs, players then have a dual purpose to their play, for not only will their player characters and henchmen gain levels of experience, but their actions have meaning above and beyond that of personal aggrandizement.