طَابَ زَيْدٌ نَفْسًا
Translation: Zayd is good in disposition.
طَابَ: past verb, built on fatḥ, expressing goodness.
زَيْدٌ: nominative subject by ḍamma.
نَفْسًا: accusative tamyīz of a sentence relation; it specifies disposition.
Remove nafsan and the respect in which Zayd is good becomes unspecified.