David Ortiz thinks he knows why the Chicago Cubs haven't been able to win consistently.

Ortiz, who stands as Theo Epstein's biggest acquisition during the Cubs president's decade as an executive with the Boston Red Sox, blames the one thing many Cubs fans cherish -- the one thing that sets the Wrigley Field experience apart.

"Through the years I've talked to a lot of friends of mine that have played for the Cubs," Ortiz said Tuesday night before the Red Sox lost 2-1 to the Cubs in the second game of a three-game series at Fenway Park. "The one thing that everyone talked about was the schedule in Chicago. They get excited walking into a city that's based on baseball, but once they start dealing with the schedule it kind of mentally wears you down."

Ortiz cited former Cub Alfonso Soriano among others who haven't liked the mixed schedule of day and night games.

When the team first installed lights in 1988, the Cubs were limited to 18 night games due to their stadium being in such proximity with the neighborhood. Over the years the city had increased the number to 30 and for the first time in 2014 the Cubs have 38 scheduled night games.

"Believe it or not that's one of the biggest issues for that organization to become a winning ballclub," said Ortiz, who signed as a free agent with Epstein and the Red Sox in 2003 after six years with the Twins. "When you come down to the Cubs' schedule it's a game-changer, believe it or not. They play so many day games at home and then they have to travel to another city and adjust themselves to the night games."