Ironman
The purpose of Ironman mode is to help the single player gamer to resist the urges to correct mistakes and change decisions already made. It is the ultimate challenge for you to ride out history’s waves and tumults.
In practice this means that EU4 itself will save the game at various points using only one and the same save game, thus removing the option to save the game, experiment with a course of action and then reload when your plans blow up in your face.
Playing an Ironman game is meant to be a bit of a challenge so some other game settings will be disabled or locked and of course _NO_ cheating is allowed. Not that any of you would cheat.