One of the Hawks' premier midfielders, Day had to sit out the club's brave finals runs in 2024 and 2025.
The 25-year-old has been plagued by foot and shoulder issues, until an uninterrupted run since returning in round 12 this season.
The 88th game of his AFL career will be Hawthorn's qualifying final against minor premiers Fremantle at Optus Stadium on Thursday night.
"I mean there was definitely some times where you felt really defeated," Day said.
"You come back, you put everything into your rehab, and then to go down with another injury, you do feel really helpless at times.
"At times you think, 'Oh, is this just me?'
"But to keep going and really push through, I think it'll make this final series even sweeter.
"Since I've been back from this shoulder, I've just been really grateful to be back playing, and then to be able to do that in September with a bunch of mates that I love so much is going to be pretty cool."
Hawthorn were in front at quarter-time of last year's preliminary final against Geelong, before being brought unstuck by a Patrick Dangerfield masterclass.
Hawks fans couldn't help but wonder how the result would have gone had Day been available.
"It was pretty tough at the time," Day said.
"You work all year, and I had both of the injuries pretty late in the year.
"To watch them go out, obviously supporting them, but not being able to help was the toughest thing."
Hawthorn's medical staff have carefully managed Day since he returned to the team in May.
"I've got the most confidence in my body I reckon I've had for my whole career,'' Day said.
"The off-season we were managing the foot and did a really good job of that.
"Then when you go down with the shoulder, it actually gave us more time to really get the foot right."
Day believes Hawthorn have defied the critics who believed they should have tried harder to bring in Zach Merrett in the last off-season to bolster their midfield.
Merrett is again expected to request a trade to the Hawks, but a deal will almost certainly get done this time.
"There was a bit of a narrative last off-season that it was needed (to recruit Merrett)," Day said.
"We're proud to show that this year we've been able to step up as a midfield group, probably more as the season's gone on.
"We've been able to prove that it's probably not as much as a necessity now, probably more of a want (to get Merrett)."
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