The beauty of that sunset was unrepeatable - we'll never witness the exact same scene again.

unrepeatable 是由前缀 un-（表示"不、非"）加上动词 repeat（重复）和形容词后缀 -able（能够...的）构成的形容词。字面意思是"不能被重复的"，引申为"独一无二的、无法复制的"。