We had a lot of those games, especially during the Derek Dooley and Butch Jones era. (Pruitt era was pretty bad, we were just getting blown out most games. This is why I think he was the worse of the three despite having a better overall record than Derek Dooley).
It takes a lot of bad luck to struggle as well.
A classic example that makes me think people were too hard on Dooley was the fact that most of our SEC West draws were rough. During the Derek Dooley era where we went 5-7, most of our opponents were in the top 10-25 rankings. We had the bad luck of catching Arkansas, Ole Miss, and Miss State during times when they were at their height. For example, we played Miss State when they had Dak Prescott and went 11-2 and with the exception of Dooley's first year, we captured Ole Miss when they were in the top 10. South Carolina during that era had Steve Spurrier and was having their best run while Missouri had Gary Pinkel and Vanderbilt had James Franklin.
There were a lot of games that came down to turnovers, missed FGs, bad calls etc.
Even this past season, the Pittsburgh and Purdue game had several bad calls or no calls at the end that impacting the game while a TD in the Ole Miss game was called back incorrectly.
2015 was a classic season for Tennessee that could have gone very differently. A couple of bad calls and some bad luck plus grit by Oklahoma allowed them to comeback and win in OT in Knoxville despite being down 2 TDs late in 4th quarter. We had a hail mary play against Florida that depended a lot on luck (and blown coverage), the Alabama game was also very close that year. Change 3 plays and Tennessee is likely 11-1 and a playoff contender in 2015.
I see the same situation with Nebraska last year where a lot of games could have gone the other way so perhaps Nebraska isn't as far off as people think.