Piece vision: what attacks what

Piece vision is the habit of scanning, every move, which pieces attack which — and whether each attacked piece is defended. A piece that is attacked and NOT defended is 'hanging': free to take.

In the diagram, White's rook looks straight up the open e-file at Black's bishop on e5. Nothing defends that bishop, so it's hanging — White just plays Rxe5 and wins it for nothing. Train your eye to find loose pieces like this on every single move.