Textbooks often introduce い and な adjectives, which “only differ in their ending”. However, that is not the whole truth.

Differences §

• な-Adjectives are essentially nouns, not real adjectives
  • -> require です・だ or な(“glue form” of だ, see です and だ explained)
• い-Adjectives are very similar to verbs (due to Japanese conjugation)
  • -> don’ t require です・だ