re: Poker & ICM QUESTION
yeah get used to it, quit doubting until you have real evidence to suggest that you are doing something wrong. By real evidence i mean HUD tracker stats or out of game reasearch, when you are in game you want to be fully confidant in what you know in that game.. then once you have finished, be completely the opposite of confidant, question everything and try to get better.
In game if you find spots that worry you or you are completely lost with what to do, make a note of that spot and try to learn about it to improve your knowledge. Just like any SNG but especially DON the goal is to be able to play many, many tables, like 20+ with DON due to there not being a huge amount of decisions to make. so the more you know what to do without thinking in game the more tables you can play.
anyways before i babble anymore, be confidant in your thoughts in game, then when away from the game question things, strive to get better and learn and it will have a snowball effect with your decision making in game.