"Knowing that my body can endure a whole season and just having confidence in my head that I can handle first grade, having almost completed two seasons.
"It's something that's built character within me and I'm still learning and still trying to build the stuff around the mental side of my game."
After debuting in 2014, Fusitu'a impressed with his flamboyant finishing skills, but he found it hard adjusting to the demands of the NRL during his rookie year.
A difficult night against the Broncos at Suncorp Stadium tested his mettle, but that experience along with the support of the Warriors senior players made him aware of the standards he needed to reach.
"I had a tough day at the office and was playing through injury," he said.
"It was hard in my rookie year. I had a couple of bad games and I've just been learning from that year after year.
"The senior players really drive moving forward, leaving last week behind and looking forward to the next game.
"They do a good job in teaching me and other younger players, firstly how hard it is in this competition, but also how important it is to keep moving forward, and if you have a bad game there's things you can learn from and get better."
Fusitu'a said he was aware of the perception that he had lacked mental and physical fortitude early on and revealed he needed to overcome his own doubts as he worked to prove his critics wrong.
"It has been [a big motivation]. After having so many injuries and then you get a bit of a knock, you just automatically think, 'I've done something again'," he said.
"When you're like that, in your head, you're like, 'I don't know if I can keep playing, I'm getting knocked around.'
"And in the past I've gone down, but now, knowing that my body can handle it, when I get a knock I know I'm sweet and can keep going."
Warriors coach Stephen Kearney agrees Fusitu'a has developed a harder edge but believes he's only just beginning to realise his potential.
"That's certainly been an improvement area for him," said Kearney. "We're all well aware of what David can provide the team, when you see him scoring tries and jumping for balls. I think last week the game required him to carry the ball really tough out of the back-field and he did that pretty well.
"He's made some real progress over the last couple of weeks to be fair and we keep on David to keep doing that so he becomes a consistent NRL player."
Newcastle Knights v Warriors at McDonald Jones Stadium, 5pm
Knights: Nathan Ross, Ken Sio, Dane Gagai, Peter Mata'utia, Shaun Kenny-Dowall, Brock Lamb, Trent Hodkinson, Daniel Saifiti, Jamie Buhrer (c), Josh King, Sione Mata'utia (c), Joe Wardle, Mitchell Barnett.
Interchange: Danny Levi, Luke Yates, Lachlan Fitzgibbon, Jacob Saifiti, Jack Cogger, Sam Stone, Brendan Elliot, Chanel Mata'utia.
Warriors: Roger Tuivasa-Sheck (c), David Fusitu'a, Blake Ayshford, Solomone Kata, Ken Maumalo, Kieran Foran, Mason Lino, Jacob Lillyman, Issac Luke, Ben Matulino, Isaiah Papalii, Bunty Afoa, Simon Mannering. Interchange: Ata Hingano, Sam Lisone, Ligi Sao, James Bell, Jazz Tevaga, Tevita Satae, Nathaniel Roache, Charnze Nicoll-Klokstad.
Referees: Chris Sutton, Chris James.
