Yost, however, didn't give up on the idea.
And when Nori Aoki went on the 15-day disabled list 10 days ago, creating that void in the No. 1 spot of the Royals' lineup, Yost went back to an old experiment, inserting Cain back at the top of the order.
The skipper was looking for anything that might provide some life for the offense and give Kansas City an edge in its effort to build off last year -- the second winning record in two decades -- and help the club advance to the postseason for the first time since 1985.
With their first walk-off victory of the season -- 5-4 over the Angels -- on Sunday afternoon at Kauffman Stadium, the Royals are very much in the postseason hunt, just 3 1/2 games back of American League Central-leading Detroit and 1 1/2 games behind Seattle for an AL Wild Card berth.
And Cain showed on Sunday that he can provide an impetus, atoning for a misplayed fly ball that led to a first-inning run by going 4-for-5 with three doubles and two RBIs in the midst of a four-run fourth inning that allowed Kansas City to take a 4-3 lead.
"I told him that I didn't want him to change a thing," Yost said. "I want him to stay the way he was hitting in the six- or seven-spot. He was swinging well.
"I don't want him taking pitches and looking for walks. I want him to stay aggressive."
And Cain has done just that. Call it a lesson learned.
Cain had a 10-game audition at the top of the lineup last year. It wasn't pretty. Cain hit .147, had a .216 on-base percentage and struck out 10 times in 34 at-bats.
Forgot the distractions this time. Cain has.
Nothing has affected Cain, not even that costly fielding. With two outs, a runner on first and the Angels up 1-0 thanks to Kole Calhoun's leadoff home run, Cain called off center fielder Jarrod Dyson on a two-out Howie Kendrick fly ball and then, at the last second, he caught a glimpse of Dyson. Cain stepped back, letting the ball fall for a run-scoring error.
"My fault," Cain said. "I called him off. Miscue on me."
That's the only mistake made by Cain. He had the two RBIs on a double that tied the score at 3. Cain also singled to lead off the first, but he was the victim of an inning-ending fielder's choice. He then doubled with one out in the third, but he never got past second. And Cain doubled to lead off the sixth, only to be stranded there when Kevin Jepsen struck out Eric Hosmer, Billy Butler and Alex Gordon, the next three batters in the lineup.
"I am trying to stay with my approach, hitting the ball all over the park, getting on base so the guys can drive me in," Cain said.
The payoff is in eight games hitting leadoff, Cain has hit .407 with a .412 on-base percentage thanks to one walk. He's scored four runs, but he also has driven in six, providing a late-inning bonus for Yost, who now has somebody with the ability to drive the ball at the top when the lineup turns over in late-inning situations.
And Cain's done it against left-handed pitchers as well as right-handers. He has a .381 on-base percentage against lefties and .359 with right-handers.
Who knows what will happen when Aoki is ready to return. Aoki may be more of a threat to steal bases, but he was only hitting .263 and had a .326 on-base percentage, with 14 extra-base hits in 262 at-bats.
Right now, the Royals are just enjoying the spark from Cain.
Cain's shortcomings of the past have fed into the success of the present.
"Last year, I thought I had to see every pitch," he said. "I'd have long at-bats, I'd go to 3-2 and then ... I'd get in trouble. Pitchers are so good. They'd know you are taking early in the count, and they challenge you more.
"This year, I try and go up and see the pitch and hit it, just like I would in any other spot."
It's just like Yost and his staff have drawn it up.
Now, it's only been seven games, and Kansas City is only 3-4, but the concept, which also included putting Hosmer into the No. 2 slot, has been well received.
"When [Cain] gets on, there's always that chance he will get that extra base, force the defense to do something," Hosmer said. "He is fast and he gets on base. And right now, he is clicking."
Cain leads the Royals with a .322 average, the only regular hitting .300, and is hitting .433 with runners in scoring position. He is also tied with Hosmer for third on the team with 35 RBIs.
"With Nori down right now, we need a spark, and he has given us one," Hosmer said.
Cain has given the Royals just that.