Lester, 37, was never offered much in the way of a new contract with the Cubs before signing a 1-year, $5 million deal with Washington.
"It's natural," Lester said. "I had to get over some stuff leaving Boston. Chicago was my home for six years. We have a house there. My kids grew up there. You invest in a city, you invest in that place that you're working. Yeah, there's emotions involved."
Lester is often cited as arguably the best free-agent signing in franchise history, but nostalgia couldn't keep him a Cub. After the team declined a $25 million team option for 2021, the 16-year veteran sat and waited for a new offer that never materialized. Worried about how late it was getting in the offseason, Lester signed with the Nationals.
"The hard part of this game is the business side and you have to separate your heart and business," Lester said. "Sometimes that can be difficult. It's only natural to go through a phase where you question certain things, but once you separate that and realize it's a business ... it is what it is."
Lester is happy to be pitching on Monday, in the opener of a four-game series. He can get it over with and then relax and visit with friends with whom he won a World Series in 2016, breaking a 108-year championship drought for the franchise. But he's most excited to see a fan base he never got to say goodbye to last season due to COVID-19 protocols.
"I look forward to it," Lester said. "I'm glad fans are in the stands. It'll be nice to see the faces in the stands and get back to normalcy there."
As for facing his former teammates, the trash-talking began in spring training as Lester is most excited about staring down first baseman Anthony Rizzo. The two share a bond; both were drafted by the Boston Red Sox and both beat cancer while with that organization.
"That will probably be the matchup that will stand out the most to me," Lester said. "I might have to invent something out there. I'm pretty much inventing stuff as I go as it is. Maybe throw a knuckleball or two or mix something in like that."
Lester won 77 games for the Cubs, including Game 5 of the 2016 World Series against the Cleveland Indians, then came on in relief in Game 7, which the Cubs won in 10 innings. It cemented his legacy in Chicago.
He was asked what it means to be considered such a great free-agent signing.
"It's a huge compliment," Lester said. "I don't know if it's true. It's flattering."
Lester will see his former catcher in the Cubs' dugout: David Ross is now the manager of his former team. The two are close friends.
"The guy is super special to me," Ross said. "I hope the fans give him the welcome back he deserves. He means a lot to this organization. I think fans recognize that. Cubs nation that I know will be super appreciative and give him the love that he needs."
Besides pitching against the Cubs, Lester's biggest concern is finding where he needs to go when he gets to Wrigley Field.
"The biggest thing for me is making sure I walk into the right dugout," he said.