The 2016 season hasn’t started yet, but we already know one thing; everyone loves the Cubs this year. Whether you go by projection systems, gambling odds, expert predictions, or general pre-season hype, it’s pretty clear that the Chicago Cubs are the team to beat in 2016. Our forecasts expect them to win nearly 60% of their games and our playoff odds give them a 94% chance of reaching the postseason. Expectations couldn’t really be much higher.

But if there’s one thing baseball is particularly good at, it’s reminding us all how uncertain we should be about predicting a specific future for one player or even one team. In the aggregate, we can do a decent job of forecasting large groups, but for individuals or single teams, the range of possible outcomes is still really large. Last year, for instance, the Nationals had almost exactly the same projections as the Cubs do now, with a .585 projected winning percentage and a 94% chance of reaching the postseason. But instead, they won 83 games and watched the playoffs at home.

So, before the Cubs start playing games that count and things start threatening to go wrong, let’s take a look at what could cause the Cubs to follow in the Nationals path.

Before last season, Jake Arrieta had never thrown more than 175 innings in a season, but including the postseason, he threw 249 innings a year ago. And while he looked remarkably dominant at the start of the playoffs, by the end, it seemed like it might be catching up to him. Here is his fastball velocity chart, by game, from last year.

The Cubs have taken it easy with Arrieta this spring, as he’s only thrown 11 innings in spring training — for comparison, Kyle Hendricks is at 25 — and are likely to manage his workload more carefully this season if they have the opportunity to do so. The link between innings pitched and arm injuries is still not all that well understood, but the Cubs are probably wise to be aware of Arrieta’s workload, as his dominance is a large part of why they’re projected to be so good.

If Arrieta’s arm gives out, the Cubs aren’t exactly screwed, but he looks like a five win pitcher, and while Adam Warren is a nice depth option to have around, that’s still a big drop-off. Not to mention that taking Warren out of the bullpen to replace Arrieta would weaken the team’s relief corps, and in a rotation where the back-end guys have historically not worked deep into games, losing Arrieta could tax the bullpen in a significant way.

The Cubs could survive losing Arrieta, but if things go off the rails in Chicago, it seems pretty likely that he’ll either have gotten hurt or pitched significantly worse than he did a year ago.

The Cubs paid a significant price to add not only Jason Heyward’s bat to their line-up, but also his glove to their outfield, as he’s been one of baseball’s premier defenders for the last five years. The Cubs are looking at Heyward as a good hitter who turns himself into a star by virtue of excelling at the other parts of baseball, but if the defense regresses, he’s more of just a nice player than any kind of franchise cornerstone.

And it’s not totally unheard of for defensive value to erode quickly. Jacoby Ellsbury was an elite center fielder in Boston, but has been graded out as average-ish since joining the Yankees. Going a little further back, Carl Crawford put up a +52 UZR in his final three seasons with the Rays before putting up a -4 UZR in his first season in Boston. Gerardo Parra was graded out as one of the best defensive outfielders in baseball from 2010-2013, then rated as average in 2014 and awful in 2015.

More likely, Heyward is young enough to avoid those sudden collapses in defensive value, but he’s a big guy with a history of injury problems, and if he tweaks his knee or strains a hamstring, he could lose a big part of his game in a hurry. With below average defenders in the other two outfield spots, the Cubs are counting on Heyward to help run down some of the balls in the gaps, but if that doesn’t show up in Wrigley, the pitching staff might get frustrated whenever a ball gets hit in the air. You can win with lousy outfield defense, but it’s certainly more difficult than if you have a guy out there running stuff down and helping his pitchers out. If the Cubs season collapses, don’t be surprised if we’re left trying to figure out why Heyward stopped being an elite defender upon his arrival to the north side of Chicago.

Kris Bryant was an absolute monster as a rookie, putting up a 136 wRC+ while playing surprisingly good defense at third base, and even ranking as one of the game’s best baserunners as well. He lived up to the hype and then some, and he got better as the year went on, finishing with a 186 wRC+ in September. After just one season, Bryant looks like one of the best players in the game.

But his overall excellence overshadowed the fact that Bryant does have a flaw; he swings and misses a ton. He only made contact on 66% of his swings last year, the lowest rate of any player in baseball. A 66% contact rate is at the bottom edge of what big league hitters have ever done, and the guys who have lived in that range — Giancarlo Stanton, Chris Davis, Ryan Howard, and Josh Hamilton being the most successful names in that group — have had some ups and downs as their power bounced around. To succeed while whiffing on every third swing, you have to maximize your productivity on contact, and that isn’t always easy.

The other guy who ran a 66% contact rate last year? Joc Pederson, who bombed his way into the All-Star Game with a 137 wRC+ in the first half of last year, but put up a 79 wRC+ as his power abandoned him in the second half. Bryant should have a higher floor than Pederson because he hits more line drives and fewer fly balls, but there’s a pretty significant risk with guys who swing and miss this often. And a lot of Bryant’s offensive value was because he ran a .378 BABIP last year, which won’t last.

While we shouldn’t expect a total collapse, Chris Davis’ 2014 season is a reminder that Bryant could end up taking a big step back this year if the power regresses and the BABIP collapses. More likely, he’ll still be an excellent player even with some BABIP regression, but the low contact rate at least seems to open the door to pitchers figuring him out in a way that leads to a prolonged slump. And if Bryant isn’t an offensive force in the middle of their line-up, that offense suddenly looks a lot less scary.

The Cubs are deep enough to overcome any one of these issues, and probably even two of them. But if Arrieta goes down, Bryant’s contact problems are more significant than is currently being talked about, and Heyward’s defense goes the wrong way, the behemoth of the NL Central could find themselves looking up at St. Louis and Pittsburgh.

Of course, we could do this same exercise with any team in baseball, and it’s even easier for the other 29 clubs. The Cubs have more depth than almost everyone, and they have so many terrific players that they could lose one or two and still be a contender. But as we head into the season of the Cubs, it’s worth a reminder that they aren’t invincible. They look like the best team in baseball heading into the season, and I think everyone is correct in identifying them as the team to beat. But often, baseball delights in humbling the favorites. The Cubs deserve to be favorites, but there are plenty of ways for this to all go wrong.