"I think maybe I was in the comfort zone at Penrith,'' Jennings told AAP.
"I'd been involved with the club since I was eight, and I always thought I would be there for the rest of my career.
"Looking back now, I realise my attitude probably wasn't the best and I could have done some things differently but I always gave my best for Penrith.''
Jennings' arrival at the Roosters was overshadowed by superstar dual international Williams' high-profile return to the NRL and the addition of James Maloney from the Warriors.
And he said seeing how Williams trained and prepared for games was a huge eye opener.
"It was a bit like starting school when I first came here,'' he said.
"I knew some of the boys like Mitchell Pearce, but I very much had to start again and prove myself to my teammates.
"Sonny came in after me but straight away you could see he did everything so professionally. The way he trained and how he prepared for games.
"When you see a guy as good as he is having to work hard it does rub off on you and make you think `am I doing enough?'
"I was hurt when Penrith said they were happy to let me leave as it's my club and the club my family support.
"But coming to the Roosters has been the best move of my career and I am so happy with how this season has gone for me.''
A place in the Kangaroos squad for the Rugby League World Cup is also on the horizon with long-serving centre Justin Hodges ruled out after rupturing his Achilles.
Selection in Tim Sheens' Australian squad would cap a remarkable turnaround for a player who was picked to play on the wing in the 2010 NSW City Origin team - a year after scoring a hat-trick in his single Test appearance on the 2009 Four Nations tour against France.
"It would be nice to go to World Cup, but I haven't really thought about, I am just focused on winning the grand final and if it (selection) happens, it happens,'' he said.
-AAP
