The 2017 No.1 draft pick played like he'd been shot out of a cannon in the second quarter at the Gabba in Saturday's preliminary final against Carlton.
The Lions conceded the first five goals but kicked 10 of the next 11, winning by 16 points to book a grand final date with Collingwood on Saturday.
Rayner finished with just nine disposals but his thundering impact in that term, bulldozing into packs and injecting himself at the centre bounce, helped turn the tide.
A central figure in the Lions' rebuild under Fagan, Rayner had had enough of the club's four previous finals appearances without a grand final berth.Â
"I feel like we've been given the baptism of fire for the last couple of years," he told AAP.
"Any other team after that first quarter probably thinks it's hard to get back from there but we just kept fighting and kept going and to turn that game around and give ourselves an opportunity to win it all next week, it's awesome.
"We've learnt our lesson big time and we know what it takes to get to these games now."
Fagan said Rayner had learnt to inject himself at crucial moments this season, revealing he had a licence to attend the centre bounce whenever he felt it necessary.
"That's why we drafted him No.1, he's so dynamic," Fagan said.
"He's maybe not as consistent as people would like him to be.
"Where he plays, mostly as a forward, it's not easy to be in the game all the time but (in the second quarter) it looked like he took it upon himself to turn the tide.
"He picked his moment."
Brisbane finished last in the season before Rayner joined, the low point after a mass player exodus in 2013 drastically impacted the club.
The 23-year-old missed his entire fourth season with a knee injury but directed his joy to the players that have been at the club over the full journey.
"Froggy (Ryan) Lester, Dayne Zorko and some of those older fellas, to do it with them at this club, to get here as a competitive, well-respected club when we were on the bottom of the ladder is a credit to everyone and super exciting," he said.
Fagan said there were no issues with star midfielder Lachie Neale's shoulder after he had grabbed at it in the second half and that key defender Jack Payne could still prove his fitness for the grand final after missing the Carlton clash with an ankle injury.
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