In any season, unless you lose half of your team suddenly, when you are 8-5 with control over your destiny and you lose your last three games to miss the postseason, it has to be a disappointment regardless of the circumstances that led up to your 13-game record.
That was the case for the Pittsburgh Steelers last year, who astoundingly weathered the loss of Ben Roethlisberger, and then the benching of Mason Rudolph, to bounce back from a 1-4 start to reach that point, on the strength of a 7-1 run in the middle of the year.