For Pete Crow-Armstrong, learning what it will take to be successful in the big leagues started quickly.

The Cubs’ top prospect (and No. 12 in baseball, per MLB Pipeline) was called up on Sept. 11. He made his debut later that night when he pinch ran in the top of the seventh in Colorado. In the minors, he had loads of baserunning success (71 stolen bases in 214 games). With the Cubs in the heat of a playoff push, utilizing that area of his skillset (plus his defensive prowess) made a lot of sense.

After moving to second base with one out in the inning, Crow-Armstrong looked to put that on display. He’s become known for his aggressive approach on the basepaths aided by his immense speed. And when the count on Christopher Morel reached 0-2, he tried to put it to the test in the majors for the first time.

The result was not what he envisioned. Rockies catcher Elias Díaz fired over to third, catching Crow-Armstrong trying to swipe the bag. Instead of moving himself closer to home plate, or just staying in a spot where a base hit likely drives him in, he had to walk back to the dugout.

The initial taste of big league action was obviously a bit sour.

“I think I had a really good idea of of tendencies, I guess, from certain guys in the Rockies’ bullpen after one session of sitting down with Nap [first-base coach Mike Napoli] and kind of going over how to pick things out,” Crow-Armstrong said in a conversation with CHGO last weekend in Milwaukee. “But I didn’t execute it the right way.”

The 21-year-old, affectionally known as “PCA” by Cubs fans, learned throughout his first three weeks in the majors just how different things are. That play in Denver served as a wake-up call that not everything he did successfully while moving through the system will work at the big league level.

“That kind of just showed me that you have to be on your shit every second of this game,” Crow-Armstrong said. “Because when I want to steal a bag, I can’t really rely on my athleticism and speed anymore. It doesn’t work, because a lot of catchers like that are going to eat you up and spit you out if you don’t do things perfectly. I think that was a pretty good introduction into being like, hey, your preparation means more than almost anything. It sets you up for success.”

That first caught stealing wasn’t the only time Crow-Armstrong struggled during his first stint with the Cubs.

He had some amazing moments, for sure — who could forget those catches he made in the spacious outfield at Coors — the kind of moments that reminded fans why they should be so high on him. But his aggressiveness on the bases also got him into some trouble along the way, and his bat never quite looked major league ready.

Not that anyone expected him to come up and set the league on fire. Especially not when you take his role on this year’s Cubs team into account.

Crow-Armstrong was brought up for his baserunning and defensive prowess. That’s why he only started three of the 13 games he appeared in (just two coming before the Cubs were eliminated from postseason contention), with the others coming as a pinch-runner or a defensive replacement. In the minors, he was playing basically every game and getting daily chances to work through any struggles. But with the Cubs, his playing time was inconsistent. Winning was prioritized over development, and Crow-Armstrong wasn’t going to be afforded a bunch of opportunities he didn’t earn.

Adjusting to the majors is difficult for any rookie. Doing that while also learning to contribute in limited action during a playoff race presents another challenge. That had to be tough for him, right?

“Yes and no,” Crow-Armstrong said. “I think it was difficult for a second, just because I had to figure out what routine works for Pete Crow-Armstrong, the rookie who has a more specific role now. Playing every day, you get used to it and you get in your routine in each week you play down there. … So, I guess that would be the yes part of it. But no, because of the help and the guidance and people just vocalizing to me that I’m here for a reason and a purpose.”

Again, he had his issues on offense. He looked overmatched against major league fastballs in particular, posting a 51.7 percent whiff rate and only a .140 expected batting average on the pitch. He’d hit well at every level in the minor leagues, but in his short time with the Cubs, that didn’t manifest into much offensive success.

But that experience in itself might still benefit him in the long run.

“I sat down with him on Sunday and told him this: I actually believe that will end up being the single best thing that could happen to him, in a lot of ways,” Cubs president of baseball operations Jed Hoyer said during his season-ending press conference. “He is a good hitter. I think he’s probably realized that he has to make certain changes offensively, and I think realizing that now is really key. This is the big leagues. This is the best league there is, and the pitching is a lot better than it is in the minors, and I think seeing that up close and personal and realizing, ‘OK, there’s probably adjustments I have to make.'”

For Hoyer, that also brought back memories of a young first baseman getting his first shot with San Diego in 2011 (for whom Hoyer was then the general manager).

“I watched Anthony Rizzo hit .141 over roughly 150 plate appearances in 2011,” said Hoyer in his message to Crow-Armstrong. “He was a top prospect. He had incredible minor league numbers. He came up to the Padres and literally hit .141. He looked terrible, and we sat him down at the end of the year and said, ‘OK, you saw what it’s about. You have to go make real changes.'”

The Cubs acquired Rizzo before the 2012 season, after Hoyer had joined the front office. What he then saw was a player who’d truly listened to that feedback, as “he had completely altered his swing” when he arrived to Cubs spring training and hit .285 after being recalled later that summer. But as Hoyer noted, “There’s no way he makes those changes if he doesn’t struggle.”

“Struggles are really, really hard to watch and struggles are hard to go through as a player, Hoyer said, “but if you take them to heart and you’re willing to go work on it, I think it can be the single best thing that ever happened. I really believe that.”

At such a young age, Crow-Armstrong seems to already be a pretty mature self-evaluator. He said he had conversations and received feedback from plenty of Cubs players and coaches. He also mentioned “checking off boxes” in terms of having different experiences, both positive and negative, that will now drive his offseason.

He’s already making a plan on specific things he wants to work on, too. That includes finding more consistency in his swing and his routine and striking the right balance between “too much tinkering to not enough tinkering” with them. He’s also looking to get better on going back on balls hit straight over his head (which is sort of refreshing to hear from someone with a rare 80-grade on defense).

Might it have been a bit humbling to take his lumps during his time with the Cubs this season? Possibly. But for both Crow-Armstrong and those who have high hopes for him, learning what he needs to do to make it at this level will be extremely beneficial for his future.

“Certainly, I wish he’d come up and hit .500 and led us to four more victories,” Hoyer said. “That didn’t happen, but second to that, having that experience where I think he’s going to take that to heart and go make those changes I think is really important, because he’s going to be a good and very impactful player in this league for a long time.”