Probably one of the best dramas ever. This drama mostly has rookie actors but their level of acting is just too good. The plot is also really good and unique. It focuses on the life problems of deaf people as well as a strong bond between a son and a dad. As well as the story portrays a really good relationship of eomma and appa, their history is also too good. They used the concept of time travel which included mystery, plot twists, loving relations, friendship, having a shining youth and what not! Not only this it also encourages people to learn sign language. The only con is that they ended the show too quickly without properly wrapping up everything. They did not show what happened to Se gyeong and Eun yu. They could have also added the college scenes of Yi chan and Chung Ah. They also did not add how Chung ah supported Yi chan, how their relationship grew, What problems did chung ah face after becoming the chairwoman. They could have even deleted the kiss scene at the last.This is the reason why I have given it a 4 star. If (it is probably impossible) they release one extra episode showing all this, then my rating would probably change. But rn it is 9.5/10. Anyways, it's a must watch. It is really beautifully portrayed with a happy ending.