It is self-evident that hard work is the key to success.

self-evident 是由 self（自己）和 evident（明显的）组成的复合形容词。self 表示"自身"，evident 来自拉丁语，意思是"明显的、显而易见的"。 self-evident 字面意思是"自身就明显的"，引申为"不言而喻的、显而易见的"。