"I hate boring books."
Translation:저는 재미없는 책들을 싫어해요.
Pronouns, whether they be first person or not, can be optional at times, but definitely not always.
From Basics 4 skill tips and notes:
*Where is the subject?
When the subject (or any other sentence component) is well implied in the context, you may freely drop it in Korean, though you will mostly see and be asked to submit full sentences here since translation exercises do not come with any context. If you come across an incomplete sentence in this course, then the dropped component is probably people in general (often translated to one or you), or something very obvious even without context.