That increased confidence was evident in the 21-year-old's performance last season.
It's one reason why he is a chance to be selected in the 2013 NAB AFL Draft on Thursday night.
He attacked aerial contests with force, using his physicality to outmuscle opponents, and hit the right options coming out of defence.
Sully's opportunity presented itself at the start of the year after a reshuffle in defence and he grabbed it with both hands.
His form did not surprise Cats VFL backline coach Max Rooke.
"We put it on him at the start of the year and sort of let him know that the spot was there if he really wanted it and he just knuckled down and played some really good footy," Rooke told AFL.com.au.
Sully was a key pillar in the Cats' miserly defence and earned a place in the 2013 VFL Team of the Year – taking it to his opponent week after week.
"That's something he (Rooke) is really big on," Sully said. "Just being proactive and beating your opponent."
It's a mindset that has come with experience and learning for Sully, since his move down to Geelong from South Warrnambool.
"When he first came down we saw that in him, but he just didn't always produce it every week I suppose you could say," Rooke said.
"This year it clicked with him a bit, I think, and he's obviously matured a bit and he was able to do it more consistently.
"He's definitely got that (physicality) in him, it was just a matter of getting him to understand that he needs to play with that sort of aggression all the time."
However, Sully is realistic about his chances on Thursday night.
Sully's returned to country Victoria this week where he has taken his mind off things by driving a tractor - crushing up rocks - on a farm in Portland.
If things don't eventuate on Thursday night, Sully plans to once again set about improving on his game at the Cattery next season.
Nevertheless, Rooke is hopeful a club will give Sully an opportunity.
"I think he's just come from a fair way back but he seems a lot more comfortable now," Rooke said.
"I definitely think if he knuckles right down, again, and just keeps working at his game he'll be good enough and I hope for his sake he does get picked up."