Sustained success? Since championship, Cubs learn it’s harder than it looks

“Nothing is promised in this game. Nothing is promised in life. Teams that think they have these sure-fire, five-year windows have often seen them slammed shut in front of them through bad luck or performance or bad decision-making. We don’t take anything for granted.” — Cubs president Theo Epstein, the day after the team was eliminated by the Mets in the 2015 playoffs.

Watching the Cubs struggle through starting-pitching slumps and feast-or-famine hitting through the first quarter of the season, it can be easy to overlook what they have pulled off in the last three years, to forget that the high levels of angst are only as high as the expectations created by the success.

‘‘It’s really difficult to do that,’’ Cubs manager Joe Maddon said of a three-year run that has featured six rounds of playoff victories in eight played.

The Cubs’ homestand this week against the Indians and Giants — two of the teams they beat during their 2016 World Series run — offers two examples of just how difficult.

And maybe a reminder or two for the Cubs about what they face trying to go deep again for a fourth consecutive year.

‘‘It’s not an easy thing to do, in general, to win,” right fielder Jason Heyward said.

Yet when a Cubs team loaded with rookie hitting talent lost to a Mets team loaded with young power pitching in 2015, the

assumption was that the teams would be annual October combatants for years.

Anybody seen Matt Harvey lately?

The last time the Indians played at Wrigley Field, they won two out of three to take a 3-2 lead back to Cleveland in the 2016 World Series. The rest of the series is one of the greatest chapters in Cubs history — followed quickly by predictions and proclamations of a North Side dynasty.

Anybody remember the first half of 2017? Or the gassed finish last October against the Dodgers?

‘‘For anybody that has no idea, for anybody that’s reading about it, anybody that’s going, ‘This is the start of whatever,’ or thinking that you’re just going to be able to walk out of bed and do something, it just confirms how hard it is to win the World Series,’’ Heyward said. ‘‘Teams get better. Teams make adjustments every year. Every year is different.’’

Just ask the Indians, who fell short in the playoffs last season, entered this season as one of the favorites in the American League and enter this two-game series with a losing record (22-23).

Or ask the Giants, who won World Series championships in 2010, 2012 and 2014 but failed to make the playoffs at all during the odd-numbered years in that stretch, in part because of the toll of previous Octobers. After the Cubs scored four runs in the ninth inning of Game 4 of the National League Division Series to eliminate them in 2016, the Giants struggled to the worst record in the NL in 2017.

‘‘Going to the playoffs every single year is awesome, and you don’t ever take it for granted,’’ ace left-hander Jon Lester said. ‘‘But it’s hard to play into almost November every single year and come back and recover and be ready to go for the next year. So some of those teams that do that consistently are going to have a year where it sort of falls apart, based on health [and workloads].’’

Whether a still-young Cubs core ever sees the playoffs again, the sight of the Indians at Wrigley Field figures to remind them of what it took to get to the top, if not why so many expect them to stay there.

‘‘All those expectations, we don’t look at it as a bad thing and we don’t really worry about it,’’ said right-hander Kyle Hendricks, the ERA champion in 2016. ‘‘We’ve been able to centralize everything into this clubhouse and really focus on the group here [now], and that was probably due in large part to what happened [in the World Series] in Cleveland.’’