Our next pattern to consider involves skewers where a rook has to jump out of the way and leave a piece behind it to be taken. In this first case, notice the little knot created by Black's rook and knight. Their alignment suggests the usefulness of running them through with Bd5, which wins a piece: when the rook moves, the loose knight behind it gets taken. It would be different if the rook could move and protect the knight at the same time, but it can't.
Not all skewers involve loose pieces, but many of them do; so when you see a loose piece, look for other enemy pieces on the same line—and be especially sensitive to clustered pairs like Black’s knight and rook here.