Captain Anorak's Guide to Gaming
Against the Evil of Retconning
'Retcon' is an abbreviation for 'retroactive continuity'. It is used in comics and other fiction to mean introducing something into the past of a story to justify the present.

In roleplaying the term is used rather differently: it is used to mean that the GM changes the set-up of the scenario once the PCs have dealt with it differently from what he expected.

For instance, suppose the GM decides that fighting through a dungeon containing 100 orcs will challenge his PCs without killing them off. If, after killing 50 orcs, they have hardly taken a scratch, then the GM increases the number of orcs in later parts of the scenario. If they are seriously hurt after killing 50 orcs and obviously can't handle another 50, the GM cuts down the number of orcs in the remainder of the scenario.

If I was a player in an RPG and I found out that the GM was behaving like this, I would be utterly horrified. It would ruin the game for me. It rewards tactical blunders and punishes clever play. It means that the PCs are not at any real risk.

I want to feel that there is a real risk to my character. I want to feel that I have to play skillfully, making the right tactical choices, to win. I want to feel that things can go against me: if I choose bad tactics, or if I take a risk and luck happens to go against me, then my character can die from it. Without this risk, a combat game is not exciting.