Everyone wishes they could have done something differently in their lives.
In the K-drama 18 Again, a middle-aged man on the brink of divorce suddenly becomes 18 again. South Korean actor Yoon Sang-hyun plays Hong Dae-young, who encounters his wife Jung Da-jung (actress Kim Ha-neul) as his younger self (played by actor Lee Do-hyun).
Here are five things to know about the cast and the series, which is available on Viu.
1 REMAKE OF AMERICAN COMEDY
The series 18 Again takes its premise from the 2009 American comedy film 17 Again, starring Matthew Perry and Zac Efron, but the cast says the South Korean adaptation leaves its own stamp on the material.
Kim (A Gentleman's Dignity, 2012), 42, tells The Straits Times over e-mail: "17 Again was really fun but 18 Again was remade to be warmer and more family-centred."
Yoon (Secret Garden, 2010) says of the original: "I watched it before I got married for fun, but after getting married, having children and raising them, I was able to empathise with the script more."
The 47-year-old is married to South Korean singer MayBee and they have two daughters and a son.
2 LEE DO-HYUN'S REGRET
The younger version of Dae-young that Da-jung's 37-year-old husband is trapped in is played by rising star Lee (Hotel Del Luna, 2019).
Asked if there is an age he would like to return to, the 25-year-old says: "I don't think I'll choose to wear glasses if I get to go back and be in third grade in elementary school again.
"I'm still regretting it as my eyesight got worse after wearing horn-rimmed glasses, which were trendy at that time."
3 KIM HA-NEUL'S WANDERLUST
Kim says she would like to go back to being 18, like in the drama series, and try backpacking for once.
She says: "I love travelling. And wouldn't I be happy if I could see and feel more with a healthier body?"
While both his co-stars would take the chance to return to the past, Yoon would choose to stay in the present with his family - where he is the "happiest".
4 A YOUNGER "OPPA"
Kim may be 17 years Lee's senior, but she did not feel awkward filming romantic scenes with him.
"I was worried at first because of our age difference, but he took good care of me on the set just like how an older brother (oppa in Korean) would. He was so sweet that I couldn't feel our age difference," she says.
5 GETTING THEIR ACT TOGETHER
The series sees Yoon and Lee playing the same character and they worked on aligning their performances.
Lee says: "I tried to catch the characteristics of Hong Dae-young as played by Yoon. I observed his footsteps, habits, way of speech and practised a lot in order to act it out as similarly as possible."
Yoon recorded himself to better his performance.
He says: "It was my first time taking on a role with a double, so I went through the script carefully before filming started. I was worried about my tone being different from Do-hyun's, so I recorded my own voice and practised a lot."
• 18 Again is available on Viu.