I think I played gloomhaven varying levels of wrong (monotonically decreasing) for the first 15 or so scenarios. The classic "wrong attack modifier deck", "elements only move up 1 when you generate", "Monsters cannot move through each other", "That monster has flying" are a smattering of my misread rules.

Who cares? The game was still fun, now we play more correctly (God knows what I haven't noticed I do wrong yet). I'm a firm believer in playing early, and learning from mistakes / as you go.