Stuff that assassins have that frustrate playing against them.
Rengar ulting while taking damage, Pyke abusing his passive to heal up ignite just because he is out of vision, Things like that makes playing against them super frustrating. Even Jarvan has something frustrating his E,Q. Gets CCED but still can get out of it.
Think about a scenario in which you are about to kill pyke but he just got out of vision and heals everything up.