taken from: http://www.realms.org.uk/cms/articles/social_contract_gaming
Now at this point you may be saying, "but we always go by the rules!" And if so, then good for you, that probably means your group's social agreement fits quite nicely with the rules you are using. But think back, when was the last time your GM fudged a dice roll instead of killing a character? Did you let it slide, accepting that this is how things are done, or complain that he cheated? This is a prime example of the social agreement that players should be heroic characters who don't die arbitrarily, overruling the system's rules of character death.
Does your GM allow other players to interject with cool story ideas? I do, it's not part of the rules, but it's an accepted part of the games I play in. If I did it in some peoples groups they'd probably look at me funny, why is he suggesting how his Call of Cthulhu character dies?