It's not easy to win in the NFL. No one has won back-to-back Super Bowls since the New England Patriots in 2004, and that's a lot to say. So, sometimes it's not about how much you spend or how well you draft.

But not all teams have the same expectations. That's why they bring in head coaches with a specific purpose, either to lead them to contention or at least put together the building blocks of a winning project.

Needless to say, that doesn't happen all that often, which is why the coaching carousel is a never-ending revolving door. With that in mind, we'll talk about three HCs entering the NFL season on the hot seat.

NFL News: 3 Head Coaches On The Hot Seat Right Now

3. Matt Rhule

He's been in a tough situation given the Carolina Panthers' struggles to find a franchise QB, and Christian McCaffrey's health hasn't done much to help. Still, Matt Rhule has failed to silence his doubters.

Truth be told, Rhule's so-called defensive expertise is nowhere to be found, either. So, now that he'll have his third starting QB in as many years (fifth if you count Cam Newton and P.J. Walker), patience may finally start to run out.

2. Kliff Kingsbury

Kliff Kingsbury's shortcomings in the second half of the season have become a worrisome trend, and it's been like that since his days in college. He's a great offensive mind, but he's failed to make timely adjustments when his team has needed him the most.

The Arizona Cardinals enter a make-or-break season after spending a lot of money on Kyler Murray. They need to prove that they can keep up with contenders after putting together an offensive juggernaut of a team. Otherwise, Kingsbury can close the door on his way out.

1. Mike McCarthy

Mike McCarthy wouldn't even have a job if it wasn't for that Super Bowl with the Green Bay Packers. But the game has changed, the league has changed, and the only thing that hasn't changed is his mistakes.

McCarthy's questionable play-calling hurt the Dallas Cowboys more often than not last season. They have a suitable replacement in Dan Quinn, and Jerry Jones shouldn't hesitate to pull the plug if they struggle to keep up in the NFC East.