Why is it so hard to go back-to-back?

No team in the NRL era has won back-to-back premierships. What makes it so challenging for the best team one year to remain that the next?

In this week's Powwow with Sowwow podcast, 2010 premiership-winner Jamie Soward and pan66.com stats guru Chris Kennedy go in-depth on the issue, looking at which teams came the closest and the factors at play including Origin representation, roster changes, mental fatigue and more.

The last club to go back-to-back in a united comp was the 1992-93 Broncos and back then it wasn't uncommon with Canberra (1989-90), Canterbury (1984-85) and Parramatta (three straight from 1981-83) all having won consecutive titles in the previous decade.

From 1950 to 1975, every grand final winner bar two won the next and/or previous premiership including the Dragons famously winning 11 straight titles from 1956 to 1966.

But in the modern era of professionalism and salary caps, no premier has managed to defend a crown.

Soward's 2011 Dragons looked as good a chance as any under Wayne Bennett after racing out to four points clear at the top of the ladder after 12 rounds, winning 10 of 11 games with one bye, before Origin hit.

That year the Dragons supplied eight players to Origin, winning just two of their next 11 games and finishing fifth before bowing out of the finals in straight sets.

Eight is the most Origin reps defending premiers have had to supply since the Storm had 10 players involved in 2008, while the 2001 Broncos hold the record with a massive 13 (including two Blues as well as 11 for Queensland).

Interestingly, plenty of defending premiers actually improved their ladder position from round eight through to the end of the season, suggesting an Origin drop-off may not be the primary factor in most cases.

Only the Bulldogs in 2005 and Wests Tigers the following year failed to win enough games to make the finals in the season after a premiership.

In the podcast, Soward goes into detail about the fatigue involved in starting a defending season off with a World Club Challenge, dealing with becoming the hunted as every team lifts their game to face the premiers, and the psychological challenges of lifting for another title tilt straight after enjoying grand final glory.

With last year's premiers the Roosters having hit a mini-slump right as Origin hit with a number of key players injured, the premiers' curse looks to be alive and well.