What do you think the highlight of Jason Heyward's career has been? Surely, he considers it the Cubs winning the World Series after his supposedly mind-blowing rain delay rally-the-troops speech deep within the bowels of Progressive Field. Every player will choose the time his team won the World Series, and with good reason. But I'm talking about Heyward's highlight individual moment, the moment that leaps to mind when you close your eyes and think of his eight-year career. What is his career highlight so far?
It probably has to be this, right?

That is of course Heyward's first at-bat in the Majors, on April 5, 2010, in the first inning of a game the Braves would win 16-5, a game that heralded a new talent who would surely transition Atlanta into a new generation of dominance that would last two decades. Heyward was only 20 years old when he hit that home run. He was so fantastic in Spring Training that the Braves didn't dare keep him in the Minors, and the anticipation for his first at-bat reached a near fever pitch at Turner Field. How could it not? He was a local kid made good.
Hank Aaron threw out the first pitch that afternoon, and Heyward -- who had, again, never taken a swing in the Majors -- was chosen to catch it ("Have fun. You're ready to do this," Heyward said Aaron told him, and afterward, Aaron himself said that Heyward could "help what ails baseball"). Brian McCann said Heyward was "the best 20-year-old I've ever seen," and after Heyward's homer, Chipper Jones, an expert on the topic, said "I haven't felt electricity like that in a long time." Heyward was as thrilling a prospect as the game had seen in a decade. He was going to change the sport, and it all came together on that perfect first at-bat.
Heyward was still excellent for the Braves that season -- he led a 91-win Atlanta team in bWAR and finished second in the National League Rookie of the Year Award voting, behind Buster Posey -- and he would end up putting together a .277/.393/.456 slash line, outstanding for anyone but truly remarkable for a 20-year-old. The Braves would build their franchise around him. MLB would construct marketing plans around him. He looked destined to be a pillar of the sport, a future Hall of Famer. The possibilities were endless.

But it never got better than that at-bat (again, World Series aside). That 2010 season ended up being the best-hitting season of Heyward's career. He hit .227 his sophomore season, bounced back a bit in 2012 (while not nearing his '10 levels, though he did hit a career-high 27 homers), missed a third of '13 after being hit in the jaw with a Jon Niese pitch, then put together a solid '14 season for a Braves team that, alas, was beginning to realize they didn't have a star to build around after all and maybe needed to start over.

They traded Heyward that offseason to the Cardinals, who won the NL Central, partly thanks to another solid season from Heyward. Then Heyward signed with the Cubs for $184 million over eight years the next offseason, in large part because he was only 26 years old and thus presumably just scratching the surface of his talent. By the time Game 7 of the 2016 World Series came around, Heyward was batting eighth and went 0-for-5, including a 10th-inning three-pitch strikeout that could have cost the Cubs dearly. He wasn't much better with the stick in 2017. He has yet to put up even an average offensive season since signing with the Cubs. Suffice it to say: You hear a lot less Face of Baseball, Future Hall of Famer talk about Heyward than you used to.
This isn't mean to be an indictment of Heyward, who is still skilled enough defensively to provide the Cubs considerable value. There's even a non-zero chance -- though apparently very close to zero! -- that he will have the best season of his career in 2018 (he is only 28 after all) and will opt out of his massive contract this offseason. (Though, uh, probably not.) But Heyward is nonetheless an illustrative example of the most fundamentally true axiom in baseball, in sports, in life: Nobody knows anything. You can't predict ball, but you really can't predict what baseball players are going to do, or what they are going to become. We dream on young players because the world seems infinitely conquerable: If they are this good now, imagine how good they will be. But this, alas, is not how life works.
After all, who was more projectable than Heyward? He was massive, strong, fast -- all the physical attributes you'd want in a player -- but what made scouts and executives most excited was his plate discipline. Heyward put up high walk rates from the beginning of his career, a skill that tends to age well. Add that to the power that surely would develop -- look at him, he's huge! -- and you couldn't possibly go wrong. Except Heyward regressed as a hitter rather than evolved; his long, looping swing providing countless holes for pitchers to exploit, more prone to weak ground balls to the second baseman than monster homers into the right-field bullpen. Of all the things you imagined Heyward turning into when he was 28 years old, this is among the least likely. But that's baseball. That's life.

And this is always worth keeping in mind. When we look at MLB Pipeline's current Top 10 prospects, we see them only for what we imagine them to become. Ronald Acuna Jr. is a young Gary Sheffield, or perhaps even more. Vladimir Guerrero Jr. is his dad, but with a batting eye. Eloy Jimenez is our next Giancarlo Stanton. Alex Reyes is Bob Gibson. We see them as on a constant upward swing, the One True Thing our team needs, the solution to our problems. But young players have a nasty habit of turning into just normal old boring veterans. When Heyward was one of the top prospects in baseball in 2010, others in the Top 10 included Desmond Jennings, Jesus Montero and Domonic Brown. None of those players are currently on a Major League roster. Also in the Top 10 that year: Stephen Strasburg, Posey and Stanton. We're all just guessing.
Heyward has been a phenom, a budding superstar, a disappointment, a bust, a champion, a valuable player, an overpaid mistake, the most actively pursued free agent, a contract albatross. And he's only 28. It's no wonder teams don't want to give out long-term contracts anymore. You think you can guess what a player's going to be like in 2023? We can't guess what he's going to be like tomorrow.
Jason Heyward might break out and finally become a superstar this year. Or he might get even worse. Nobody knows anything. We have to just watch to find out. Isn't it great?