Walking into a Trap!
One of the worst types of defensive blunders comes about when a player walks into a trap that has been deliberately set for him. Nothing, in fact, is so conducive to blundering as the belief that your opponent has blundered. Our powerful sense of elation blinds us to the possibility that there is more to the position than meets the eye.
In the following position, White has oblingingly left his Queen on a square where she can be captured. You would expect Black to be more careful, and before going any further, Black takes that juicy Queen, to his sorrow.