Both are melos with strong makjang elements and similar heartwarming vibes where the FL loses everything after being rich and is now living as a poor but upbeat energetic person not realizing how much her step family from her previous life ruined her life. In both there is a very similar love quadrant where FL is having this non official relationship with the SML who helped her throughout all the hardship and keeps being her doormat while waiting for her to be ready fo him while FL is falling in love with ML who is involved kind of by default and indifferently with the woman who brought FLs demise and now lives with this dark cloud over her head desperately and unsuccessfuly trying to keep ML from going to FL...

Similar plot lines with the couple meeting at different stages of their lifes where the ML loves the FL more and all the consequences of it. Don't want to give away spoilers but many similarities in the events also and similar vibes...

Even though both dramas are made in completely different setting and style they have a very similar romantic plot. Not only the story is the same - poor girl dresses as a boy for the work/study opportunity that will allow her to support her family where she gets very close with the rich ML and they fall in love, both love stories give a similar feeling, of angst and back and forth between the leads while they go through an emotional roller coaster while exploring somewhat breifly homosexuality.
They even have lots of similar scenes and plot devices.
The bromance between the rest of the gang os also cute in both dramas.

VERY similar story. Main female lead has insecurities about her looks and femininity. She meats in college "the hot guy all girls want" which went to school with her when they were kids. They become friends and he cares for her a lot while his feelings grow. Another girl from college who seems friendly at first and is after the main lead does bitchy things to her out of jealousy but she has her own problems with eating and weight... I will stop here so to not to spoil.

Very similar dramas in a lot of ways. Without giving away spoilers - the main leads stories have similarities and the same dark tone, same motives like trying to get over each other, lack of communication, dealing with loss and not a whole lot of romance, beware. The second leads serve as lighthearted romances to balance the heaviness of the main leads stories. Both dramas are very realistic with imperfect well written characters, some grow, some never change. I feel I really knew those people personally, ached with them and will miss them. Personally TTC touched my heart more.