When you play episode 1 or 4, or whatever episode you play first, you are unfamiliar with your environment. So, you click on anything and everything! And you will usually pick up important items.
But when you play your second episode, you think you know the environment so well, that you don't click on much, and you miss items, and a walkthrough is needed. At least, this happened to me.
Did this happen to anyone else?