4th year Slytherin Kim Chanmi is difficult. She wishes that her friendships weren't slipping right our of her hands and she desperately wanted Seolhyun to stay as she drifted away. Maintaining a relationship was so difficult, especially when you end up in someone else's bed at 2am. 

6th year Hufflepuff Seo Yuna is difficult. Days spent being a prefect that she forgets to be herself, or who 'Yuna' really even is. Knowing yourself was so difficult, not to mention catching feelings for a Slytherin who goes against everything you had known by firstly apparating into your bed one night. 

5th year Kim Seolhyun is difficult. She feared being replaced and didn't know how to balance her different relationships with people while losing her best friend. Confronting fears and overcoming problems was so difficult, and the fact another perfect prefect had been introduced was not helping her at all. 

Chanmi, Seolhyun and Yuna were difficult. So was Jimin with her graduation, Hyejeong watching her partner crumble and Solji letting go. Everyone was so difficult, but the hardest challenges are the ones that you need to overcome.