I felt like the title relates to every one of the female characters, but early on in each female character's story it seemed like there wasn't much mystery if any, so what's with the title !?? By the end I was guessing that it meant that the female lead would never know just how much the male lead had suffered, (even though she IS told by other characters). I feel like I missed something though !

Hmmm, from what I remember, what I got from the title was that if ML hadn’t caught the boss being engaged that day at the wedding boutique, and if he had not told FL about it, the FL would have not known how she was being cheated and would have lived a life of lies. The boss was gonna send her to Europe, while he would have gotten  married in SK but remain in a relationship with the FL flying back and forth, so she would have never known. (At least for a long while).

But I could be way off haha. I do prefer the title “Sunbae, don’t put on that lipstick” so much more.

Ohhhhh! I do like that explanation! Weirdly, the title hinges on an "IF"...while also being applicable to alot of "IFs" in the series :P  I also think the alternative title is better! Thank you !

The lipstick title makes more sense to me and it’s so much cuter! 

Ah! So true! Glad to know I am not alone in my thinking !