While the Cubs are one game under .500 through the first 65 games of the season, it seems highly unlikely the defending World Series champions won't improve, given how talented their roster is. Nevertheless, following a championship season with a sub-.500 record would hardly be unprecedented.
In fact, since 1980, 10 teams have won the World Series, only to finish below the .500 mark the following season.
2014 Red Sox, 71-91 
Dustin Pedroia and David Ortiz did their jobs as usual, but players like Will Middlebrooks and Shane Victorino battled injuries. Out of the race, the Red Sox traded Jonathan Lester and Jonathan Gomes to the A's before the non-waiver Trade Deadline. Even acquiring Yoenis Cespedes as part of the Lester deal didn't help matters.
2013 Giants, 76-86
Outside of Madison Bumgarner, San Francisco didn't have much starting pitching. Barry Zito and Ryan Vogelsong had ERAs higher than 5.00, while Timothy Lincecum was on the downside of his career and Player Page for Matt Cain pitched fewer than 200 innings for the first time since 2006.
2007 Cardinals, 78-84 
Even with Jose Pujols as an offensive weapon, the Cardinals had a tough time winning games. Adam Wainwright went from a closer to a solid starting pitcher, but overall, the rotation wasn't good. That's what happens when you lose Jeff Suppan, Jeff Weaver and Jason Marquis to free agency.
2003 Angels, 77-85 
It boils down to starting pitching, and that's something the Angels didn't have that year. Yes, Jarrod Washburn and John Lackey pitched more than 200 innings, but they had ERAs well higher than 4.00. The rest of the staff -- Diogenes Ortiz, Kevin Appier and Aaron Sele -- all had ERAs higher than 5.00.
1998 Marlins, 54-108 
After winning the 1997 World Series against the Indians, the Marlins traded Kevin Brown, Devon White, Moises Alou and Jeff Conine. By May of '98, the Marlins cleaned house, dealing Manuel Barrios, Bobby Bonilla, Jim Eisenreich and Charles Johnson to the Dodgers for Mike Piazza and Todd Zeile. Seven days later, Piazza was traded to the Mets as part of the Preston Wilson deal.
1994 Blue Jays, 55-60 
The Blue Jays played only 115 games because of the strike-shortened season. But the way they were going, a third straight championship wasn't going to happen. The starting pitching was in disarray. Pat Hentgen was the only starter who showed consistency, as Juan Guzman, Dave Stewart and Al Leiter all had ERAs higher than 5.00.
1991 Reds, 74-88
The Nasty Boys -- relievers Rob Dibble, Randy Myers and Norm Charlton -- weren't dominant like they were the year before. It also didn't help that Eric Davis missed a significant amount of time because of injuries.
1989 Dodgers, 77-83
They were supposed to be even better after acquiring first baseman Eddie Murray and second baseman Willie Randolph. But the Dodgers were without Kirk Gibson, the National League MVP the year before, for most of the season, and the offense proved to be inconsistent.
1986 Royals, 76-86
It was the first of 28 consecutive seasons without going to the postseason. Right-hander Bret Saberhagen, who won the Cy Young the year before, proved to be hittable. Tragedy struck later in the season when manager Dick Howser suffered a brain tumor and missed the second half the season. Howser passed away the following season.
1983 Cardinals, 79-83
Bruce Sutter had one of his worst seasons as a closer, while right-hander Joaquín Andújar lost a career-high 16 games. The Cardinals changed the chemistry of the team by trading first baseman Keith Hernandez, one of their leading RBI producers, to the Mets for right-handers Neil Allen and Rick Ownbey.