I will go step by step and show how missed execution at any one step can cause the play to break down. Let's start where almost any zone rushing play starts, by moving the defensive line. We'll assume Seattle is stretch left. Arizona is weakest against runs off left end, but Seattle is also the worst team in football at rushing off left end. That's little wonder with the revolving door at left tackle. This is one instance Seattle might be better starting Damion McIntosh at left tackle. We'll revisit that later.
At the snap, Chris Spencer and Max Unger will attempt to move the Cardinals nose tackle hard left. The goal is to jam the middle and stop the Cardinals inside linebackers from having inside lanes of pursuit. Spencer and Unger will attempt to double Bryan Robinson, the nose tackle that sees the most snaps at nose tackle. The goal is to get sufficient push that Unger can then single-block Robinson and Spencer can release into the second level and block the right inside linebacker.
Two things can go wrong. The less likely mistake is that Spencer and Unger cannot get initial push off the line and an inside linebacker is able to penetrate and tackle or reroute Jones. (Note, both inside linebackers are not likely to penetrate, the above is only an illustration on how either can.)
The more likely mistake is that Spencer and Unger do not achieve sufficient push on Robinson for Spencer to pull into the second level and block out the right inside linebacker. With that linebacker free to seal off the outside, Jones is blocked from running outside and sealed off from cutting back by the left inside linebacker. This mistake has beset Seattle this year, but Spencer is an upgrade over Steve Vallos both athletically and at powering the tackle off the line. Robinson can succeed either by pushing back Unger and Spencer, or by disrupting Spencer enough to stop him from reaching or getting a good block on the opposing inside linebacker.