In many ways, Mickelson's maiden appearance in Napa served as a microcosm for his past 10 months. He did a lot of things well, and left with a respectable T-8 finish. But he also made enough errors along the way to keep himself from ever getting closer than the fringe of contention.
Mickelson was making a rare fall start this week, his first since the 2013 WGC-HSBC Champions. He's unlikely to tee it up again until the CareerBuilder Challenge in January, meaning that his year - from a competitive standpoint - is now over.
Make no mistake, Mickelson's 2016 was nothing short of a renaissance. After combining for only four top-10 finishes in the 2013 and 2014 seasons and struggling with consistency, Lefty notched six such results last season and added a seventh on Sunday in soggy Napa. At age 46, he seems as devoted to his craft as ever.
"I don't feel like it's been physically more demanding, because maybe it's just because I'm in better shape this year than I have been," Mickelson said to start the week. "My energy level is up, and I'm excited to play."
There were plenty of highlights on the Mickelson 2016 reel, notably led by his 10-birdie performance in his epic match against Sergio Garcia at the Ryder Cup earlier this month. It was a tournament in which Mickelson was incredibly invested, for better or worse, and an outcome that he relished as a result.
But on the stroke-play side, Mickelson's best performances were tinged with disappointment.
There was, of course, his unforgettable duel with Henrik Stenson at the Open Championship, where Mickelson's score was good enough to win all but a handful of Opens - but not enough to match the Swede. And there was Pebble Beach, where Mickelson rekindled a bit of his old magic on a familiar layout but missed a short putt on the 72nd hole to lose to Vaughn Taylor.
They are results that kept a good year from becoming a great one. Mickelson's winless drought became a notable storyline many months ago, as his most recent victory remains the 2013 Open. For perspective, that spell is three weeks longer than the winless drought of Tiger Woods, who withdrew earlier in the week and whose return to competition remains in question.
The lack of hardware continues to be a sticking point, but it shouldn't distract from the fact that Mickelson made significant improvements in a variety of areas at an age when many players are simply counting the days to the Champions Tour.
While his short game has been a trademark for more than two decades, Mickelson found a way to improve his putting: from 52nd in strokes gained in 2014 and 41st in 2015 to ninth this past season. There was an even more pronounced spike in his strokes gained on approach shots, where Mickelson vaulted from 104th to fifth on Tour in a single season.
The area that remains a concern, and the issue that continued to nag him this week at Silverado Resort & Spa, is the driver, and it's an issue Mickelson fully intends to address in the coming months as he steps away from competition.
"I feel like from the irons on in after the drive, my game is as good or better than just about anybody in the world, but off the tee I'm playing from such a disadvantage that I have to fix that," Mickelson said Wednesday. "If I can fix my drive and drive it effectively, I'm very confident in my abilities thereafter, so it should hopefully be a good year."
Few knew what to expect from Mickelson entering this year, and given his stat line and performance in several of the biggest tournaments, you might have expected him to have a couple tournament victories to reflect on this holiday season.
But while the wait continues for career win No. 43, Mickelson was able to make clear and substantial strides after beginning the year with more questions than answers.
It's not the end result he would have liked, but it's certainly a start.