A perfect storm took down the Arizona Cardinals in 2012: worst-case-scenario injuries at running back, shoddy quarterback play, questionable planning for the offensive line, unexpected quarterback developments elsewhere in the division and a brutal schedule.
That last one came into focus while checking out a chart Paul Kuharsky ran on the AFC South blog. I've reproduced the chart below. This chart shows strength of schedule minus how each team's own game outcomes affected results.
The results are pretty similar to standard strength-of-schedule results. The Atlanta Falcons played the easiest schedule even when their own 13 victories and three defeats were removed from their opponents' results.
Note that Arizona and St. Louis ranked among the top three in toughest adjusted schedules. Each had to face two playoff teams from their own division. Each also faced New England, Green Bay, Chicago and Minnesota.
The won-lost-tied records displayed in the chart are the unadjusted records. The final column shows the adjusted percentage. For the Cardinals, the adjusted won-lost-tied record would be 130-106-4 (.550) once we removed their opponents' 11-5 record vs. Arizona from the unadjusted record of 141-111-4 (.559).