If events in his early life helped shape him as a person, then one moment during a standout year redefined him as a golfer.
Day finished the season on a high, winning his first major title at August's PGA Championship -- and becoming world No. 1 for the first time in September, albeit only for a week.
However, these breakthrough achievements followed one of the most difficult challenges in his professional career, when he suffered a debilitating bout of vertigo at June's U.S. Open.
"I learned a lot about how far I could really push myself, not only physically but mentally as well," Day told CNN.
The Australian was visibly hindered by the condition, collapsing several times during the tournament's second round and needing to lie on the grass to recover.
It was the second year in a row he had been affected at the golf season's second major -- in 2014 he had to withdraw due to vertigo, which causes a dizzying sensation of movement that is not actually there.
Despite its effects, Day went into the final round tied for first at Chambers Bay in Washington and ended up finishing equal ninth.
"The vertigo is a difficult thing, it just comes and goes whenever it pleases. I wasn't expecting it," he said.
"I've had it before and there have been years between stretches, and unfortunately it happened at the U.S. Open and that knocked me off my feet.
"I was down for the count for most of the afternoon on Friday's round. During the Saturday round there was a lot of times where I felt like I was going to quit.
"I said to myself, 'You know what, I've got to keep counting down the holes, I've got to keep pushing myself -- you have an opportunity to win your first major championship,' and that's what I wanted so badly.
"Unfortunately I didn't get my first major championship there but just to be able to gut it out and get through that week was fantastic."
Less than a month later at the Open Championship in Scotland, the 27-year-old missed a crucial putt on the 18th green of the final round at St. Andrews to finish an agonizing one shot behind the three leaders who went into a playoff -- with Zach Johnson emerging victorious.
However, a month after, Day finally won the first major title of his career with a comprehensive three-shot win at the PGA Championship -- and the world No. 1 ranking soon followed after victory in the BMW Championship.
While Day won two of the PGA Tour's four FedEx Cup playoff events, he relinquished top spot -- and the $10 million first prize for the series -- to Jordan Spieth after tying for 10th at Sunday's Tour Championship finale.
"It's been an amazing season for me," Day added. "It's kind of hard to sit back and reflect on what's happened.
"It's been such a busy summer for me and to be able to finish the way I have and also play great in the playoffs, win my first major, get to number one in the world, it's been so much stuff condensed into such a short little period of golf that I've played.
"It's been a wonderful season for me."