As katarina, She is countered heavily by CC, especially the ones which have no cast time. If she doesn’t use her r properly, then she will end up dying a lot due to being CC’d.

She relies on the lack of vision to roam around and acquire kills. If the enemy team sets up proper vision and has enough map awareness, they can easily stop Katarina from getting a lead.

Mispositioning and using her Ultimate R at the wrong time can make her quite an easy target for the enemy. Her Ultimate R roots her in place, so she can be targeted by a CC chain. As katarina, If she doesn't use her r correctly, then she will end up dying a lot because of being CC. She relies on the lack of vision to move and acquire murders. If the enemy team sets up a good vision and has enough card consciousness, they can easily prevent Katarina from getting an advance. Misposition and the use of her Ultimate R at the wrong time can make her a pretty easy target for the enemy. Her Ultimate R attaches it in place, so that it can be targeted by a CC channel.