An ounce of disappointment, whether in himself or his team, would send him home in a fury. He'd grind over it all night, fall asleep angry and wake up the next morning to start the routine all over again.
The joy was gone.
"I was so consumed with whether I played well," Donaldson said. "I was so upset. I didn't know if I even wanted to play anymore."
Then there was a time not too long ago when Donaldson thought the A's would quit on him.
A conversation with then-RockHounds manager and current A's bullpen coach Darren Bush had restored his passion. If you can impact the game in some way every game, Bush said, you've done your job for the day.
But Donaldson had trouble meeting those standards as well. He made the A's Opening Day roster in 2012, but struggled to contribute, batting .153 with one home run and seven RBIs in 28 games over two stints with the team before the All-Star break.
Donaldson joined Oakland for a third time in mid-August, determined that this attempt would be different. He adjusted his approach at the plate and did his best to eliminate the expectations he had placed on himself for so many years. His concern became simply earning playing time in manager Bob Melvin's lineup.
"I didn't really know what my future was going to be with this organization," he said.
Such apprehension now seems like a distant memory. One year after two separate demotions to the Minors, Donaldson is the most consistent player on an A's team with the best mark in the Majors since July 1 of last year (105-61) and a candidate to become Oakland's first position player to appear in an All-Star Game since catcher Ramon Hernandez in 2003.
Oakland's third baseman is among the A's leaders in every offensive category. He owns a team-best .316 average with 13 home runs, 53 RBIs and a .909 OPS.
"Last year, at the second part of the year when he came back up the third time, something clicked in with him and he's taken it and used it and kept it and held on to it," said A's hitting coach Chili Davis, who used to tease Donaldson that he'd be fined for charging the mound with his stride.
Davis regularly provides scouting reports of the opposing teams' pitchers, pointing out areas of attack, but late last season he gave Oakland's batters scouting reports on themselves.
That's when it clicked for Donaldson.
"This is where he's going to pitch you, because this is what he looks at," Donaldson recalled Davis saying. "I looked at it, and there were some pitches where I was like, 'Wow.' Like, I knew it, but I didn't know it was like that."
The toughest pitches for Donaldson to hit last year were above the belt. It didn't matter the velocity or the type of pitch. If it was up, he was going to struggle because of the location of his hands through the zone. Last offseason, Donaldson went about fixing that.
Donaldson went 5-for-9 with two doubles, two walks, two RBIs and three runs scored over the weekend against the Cardinals, who entered the series tied for the best record in baseball before the A's took two out of three.
He also contributed two gems on the defensive end in Sunday's series finale, toppling over the tarp in foul territory to secure a popup and lunging to his right on a sharp ground ball in the seventh that saved a crucial run.
"He does it all," said starter Tommy Milone. "Defensively, offensively. I'm sure if he pitched he'd do that well, too."
Donaldson hasn't pitched since he was a freshman at Auburn. His occupation of third base, however, is a recent undertaking.
He was converted to the hot corner from catcher during Spring Training last year, and the transition has been seamless in comparison to his offense.
The biggest giveaway is his assertiveness on ground balls. Third basemen often can't see the shortstop while in pursuit of the ball, and Donaldson occasionally cuts in front of Jed Lowrie when making plays on slow rollers that a more experienced third baseman might defer on.
"I think he's much improved over the beginning of the year, too," Lowrie said. "There were a couple balls early that he was probably too aggressive on, but I would rather him be too aggressive than just let balls go by, so I have no complaints about him over there. He's been great."
The change of position has had an effect on his offensive approach as well. Donaldson concentrated on his abilities as a power hitter throughout much of the Minors, focusing on home runs rather than becoming a more complete hitter.
"I understood that if I hit 20 homers as a catcher, there was no reason why I wasn't going to be a Major League player," Donaldson said. "But then I realized I'm not the kind of guy that wants that. I hate striking out. I really don't enjoy that -- at all. It got to the point where I said, 'You know what? I feel like I'm a better hitter than this. I don't have to try to hit for power all the time. I can get base hits, I can hit doubles.'"
Such focus has paid off for Donaldson, who would be a lock for the All-Star Game if the American League's third-base pool didn't consist of such titans as Miguel Cabrera, Adrian Beltre and Manny Machado.
Donaldson is fifth in fan voting with 827,381 votes (Cabrera leads all of baseball with 5,844,165), but he could make an appearance if the players vote him in.
He's a realist in regards to his chances of starting and said he hasn't checked the votes -- "Why would I?" he asked. "Miguel Cabrera's going to get voted in" -- but he did say an All-Star selection would be "something even I probably wouldn't have dreamt. Even just being in the talks and that kind of stuff, it's definitely humbling."
And while there's no way around Cabrera's brilliance, Donaldson has been just as essential to the success of the A's, who are seven games better than the Tigers in the standings and just took consecutive series over two of the best teams in the National League in the Reds and Cardinals.
Oakland will continue its stretch of Interleague games against the NL Central on Tuesday with the Cubs, who drafted Donaldson with the 48th overall pick of the 2007 First-Year Player Draft.
The A's success, as it has been all year, will be reliant in part on Donaldson's play. That's not a bad position to be in. If Donaldson has proven anything this year, it's that there's no quit in his game.