One root may produce two noun forms that point to opposite semantic roles. A sentence makes the contrast easier to interpret.
كَتَبَ الطَّالِبُ الدَّرْسَ
Translation: The student wrote the lesson.
الطَّالِبُ كَاتِبٌ وَالدَّرْسُ مَكْتُوبٌ
Translation: The student is a writer and the lesson is written.
ActivePassive
ضَارِبٌ — strikerمَضْرُوبٌ — struck
كَاتِبٌ — writerمَكْتُوبٌ — written
Read the relationship to the event, rather than guessing only from the shared radicals.