With age comes wisdom, just ask Marlo Thomas. The actress, who will celebrate her 80th birthday on Nov. 21, is taking a moment to reflect on who she is today and what she's learned in the 26 years following her father Danny Thomas' death. The star and producer of That Girl met up with Closer Weekly at the Paley Center for Media’s recent event Better Than Ever: Actresses Are Fighting Ageism — and Winning in NYC.

“My biggest life lesson is you should really stick to what you believe in,” she exclusively told Closer Weekly. "Everyone wants to tell you how to do things, and it’s really important that you not give up on what you believe."

marlo thomas danny thomas getty

Marlo with her father and Milton Berle on the set of That Girl.

Marlo, who was extremely close with her father, shared the advice she holds close to her heart. “When my father died, I got a letter from Mike Nichols, and it was the best advice,” Marlo revealed. “He said, ‘All the things you wish you had said, all the news, the thanks, you can still tell him — because the people we love stay with us.'"

And now, she looks at the world glass-half-full and continues to stay optimistic about her life. “My dad used to say I was born with rose-colored glasses on, and that’s just who I am,” she continued. “What I’ve found since I’ve gotten older is that gratitude has become a very important part of my life.” She shares that life with her husband, Phil Donahue, and her five stepkids.

“Phil and I have these big windows, and when I open the shades in the morning, sometimes
I look out and think, ‘I am so grateful to live in this world. And that I’m living with a man who loves me, and we’re healthy,’" she added. “Gratitude can give you some juice back."

For more on Marlo, pick up the latest issue of Closer Weekly, on newsstands now — and be sure to sign up for our newsletter for exclusive news!