If you don't mind me asking, why do you think it's a hard series to watch for you? I know many people have a problem with the very slow pacing of this series compared to most other crime shows that are much more fast-paced. Unlike most other crime shows that are very episodic and typically solves a different case in each episode so the story progresses very quickly, but this series on the other hand takes a whole season to solve just one case and the pacing of the storytelling is much slower and draggy so you really need to have a lot of patience in order to watch a series like this.
I am not the OP but from their statement, I understood them to mean that the show was difficult to watch because the actors were so good at making their pain seem real.