The overworked defender most often is a piece, but it can be a pawn as well. Look at Black’s pawn on e7 and see how it protects two pieces, the bishop and knight to each side of it. Treat this little visual formation as a sign of weakness; it means that one of those pieces has less protection than appears. Here White has attacks against both pieces and neither of them has any other defenders, so his course is clear: take one of the pawn’s protectorates; if he recaptures, then take the other. First comes 1. BxN, capturing with the less valuable piece. If Black replies e7xB, White has 2. RxB.

This time Black has no zwischenzug to offer—nothing interesting he can do with his f6 bishop after the knight on d6 has been taken. But there still is something more to notice: strange as it may seem, the whole thing works only because of White’s rook on a1. For notice that after White plays 2. RxB, Black can play Rb3, pinning White’s knight to his bishop—or skewering them; each piece is loose and time is too short for White to move them both. White can escape trouble by leaving both pieces where they are and playing Rc1, protecting the knight. But if the a1 rook were off the board or not within reach of c1, this maneuver would spoil White's whole sequence (remember that the other rook would now have moved to f6). How could you be sure to see this? By keeping tabs on loose pieces all the time. White has two of them on the third rank, a vulnerability that has to be kept in mind constantly—especially with a Black rook so close by.