Before making a hasty decision, it's wise to think twice.

think 是动词，意思是"思考、考虑"。 twice 是副词，意思是"两次"，由 two（二）加后缀 -ice 构成。 think twice 是一个固定短语，字面意思是"思考两次"，引申为"慎重考虑、三思而行"的意思。