When Lewis Hamilton crossed the finish line to take the chequered flag at the United States Grand Prix, he described capturing his third world championship as the greatest moment of his life.
He was certainly right to think that: having finally achieved the dream he had long had of emulating the success of his hero Ayrton Senna.
But with the dust now settled on the season, the world will come to look back on Hamilton's year as one that has delivered us more questions than answers about the brilliant Mercedes driver.
On the one hand, we were treated to a dazzling display of speed over the first part of the campaign: as he marched on to a run of pole positions and race wins that showed he was a much-improved driver to the one who was regularly beaten on Saturdays by Nico Rosberg in 2014.
The Spanish Grand Prix was the first weekend of 2015 where Hamilton was properly defeated by his team-mate; and his frustration was compounded two weeks later when a strategic blunder by his pit wall costs him Monaco glory.
Despite Hamilton's obvious speed though, Rosberg was able to shadow the Briton in the points standings until just after the summer break.
It was only when the German suffered an engine retirement at Monza that Hamilton could sense a proper breathing space between himself and his German rival.
When Rosberg suffered a broken throttle pedal in Russia the game was virtually up; and the door left open for the triumph in Austin that delivered Hamilton the crown.
And yet, while Austin marked the high point of Hamilton's season, it also marked a turning point in his campaign; for he would never win again.
Rosberg had not only got a grip on his Saturday performances – helped in part by set-up changes made after Mercedes' disastrous Singapore GP – but was finally driving with the precision and anger that had been missing early on.
He dared go wheel-to-wheel with Hamilton; he left no stone unturned in his efforts and it left Hamilton both baffled as to what had happened and at unease in the team.
The questions that Hamilton began asking his pit wall about why he was not winning became more intense; and they no doubt played a part in Toto Wolff's post-season declaration that if he felt his drivers' relationship started hurting the team then we would have to consider a different line-up.
Wolff's comment that “we only want to work with nice guys” was clearly aimed in one direction, but the message was pretty well understood by Hamilton – who has spent the post-season boosting his profile with a spate of appearances on US and UK chat shows.
We will not come to define Hamilton by this third world championship though, but in how he moves on from it.
If he rediscovers the brilliance with which he began the campaign, then he will surely seal his place as one of F1's all-time greats as he roars his way to a potential fourth, fifth or sixth world championship crown.
But if he stumbles; if the end of season form was not a blip; if the off-track lifestyle starts having an impact on his ability to perform, then questions will begin to be raised about if he is wasting his sublime talent.
Watching Hamilton in 2016 will be fascinating.