We have seen that the protection enemy pieces enjoy is important when planning a skewer of them. Loose pieces make the best targets. But as we also know from our work elsewhere, sometimes a piece that appears to be guarded actually is as good as loose because it is attacked once as well as protected once: it cannot survive the addition of another attacker.
It would be malpractice to proceed in the position to the left without examining Black’s king and seeing what is aligned with it—not just the bishop on b4 but the pawn on a7. It occurs to you that the pawn can be won with a skewer: Be3+. Yet then you see that the pawn is protected by Black’s rook on a1. Does this ruin the skewer? No. We know a few standard ways of dealing with this sort of difficulty; one which would work here is to loosen the target by capturing it and causing it to be replaced by a recapturing piece that then has no protection. Thus White can play Rxa7, and if Black replies RxR White then plays the skewer Be3, winning back his rook a move later with a pawn to show for it. The new point to see here, however, is that in this position none of those maneuvers are necessary—or desirable. The pawn is as good as loose, since the pressures against it are in equipoise from the start. White can just play Be3+, and then Bxa7 after the king moves. If Black then recaptures RxB, White plays RxR and has won the exchange as well as the pawn.
Be mindful not only of whether enemy pieces are protected but of how they are protected and whether that protection is offset by offensive pressures you can bring to bear on them.