4. Dan Heisman's Novice Nook

An absolute must read for all chess amateurs. I am reading his Fistful of Lessons today.
He describes a common mistake: The Quiscence Error. When the player stops analyzing thinking that the position is quiet.

Don’t stop kicking a man when he is down or, to put it more politely, When both Kings are exposed and the heavy pieces are still on the board, the initiative (or attack) is often worth everything – so you usually should keep checking (or capturing) if you can.