I fail to understand when to use nominative and when to use instrumental with this verb. In sentences like this one and "Ten kot nie jest normalny" the nominative is preferred, whereas in sentences like "Jestem małym dzieckiem" and "Ten kot jest złym kotem" the instrumental case is used. What's the difference between those?
The choice of whoever wrote this sentence was to write the default version from a woman's perspective. "idealny" would be what a man would say.
(The first Polish sentence that we put in the Incubator is the default one, it is the one that you get to translate. Then we put other versions, including "Nie jestem idealny" which is also a starred version just like this one.)