CHICAGO — Five years ago, Theo Epstein took a job that even his friends called career suicide.

A boy genius who had guided the Boston Red Sox to their first World Series victory in 86 years, Epstein chose to double down on that feat — by agreeing in 2011 to lead the colossally vexed Chicago Cubs, whose fruitless quest of a World Series championship dates to 1908, when they last won it.

When he was the newly named president for baseball operations, fans would stop Epstein on the streets of Chicago and launch into conversations that had a recurring refrain: “My dad is 87 years old and has been waiting all his life to see the Cubs win a World Series — what should I tell him?”

Seated in the Cubs’ dugout at Wrigley Field last week, Epstein said he always had the same reply:

“I would say, ‘Tell him to take his vitamins, because it’s going to be a few years.’”

Recounting those interactions made Epstein chuckle. He could now gaze across the dreamy expanse of the Cubs’ storied ballpark as it filled with ecstatic, inspired fans buoyed by the latest — and perhaps best — chance to end the team’s World Series title drought.

The Cubs, who opened the season with 22 players obtained by Epstein, have the best record in Major League Baseball. On the eve of the playoffs, they are a team deep in talent and seemingly without weakness, a roster that is a mix of youthful prodigies and wily veterans. Epstein patiently and strategically built the mosaic that is the Cubs’ lineup with one prescient acquisition after another.