Meaning:
“出道” means “debut,” “即” means “is,” and “巅峰” means “pinnacle.” Translated as “one’s debut is their pinnacle,” this catchphrase often used by Chinese netizens defines those who shot to fame with a stunning debut but haven’t proved successful later on. Another saying that’s one word different (“出道即高峰”； chūdào jí gāofēng), however, doesn’t have the implication that the person isn’t successful later on, while just emphasizing the impressive debut of a newcomer.
Example:
A: 你还记不记得有一部网络小说叫《无限恐怖》？
Nǐ hái jìbujìdé yǒu yībù wǎngluò xiǎoshuō jiào 《wúxiàn kǒngbù》？
Do you remember an online novel titled “Terror Infinity?”
B: 记得，情节和人物刻画都相当惊艳。可惜作者出道即巅峰，后面没什么优秀作品了。
Jìdé，qíngjiē hé rénwù kèhuà dōu xiàngdāng jīngyàn。Kěxī zuòzhě chūdào jí diānfēng，hòumiàn méi shénme yōuxiù zuòpǐn le。
Yeah, the plotlines and characters are superb. It’s a shame that the author debuted at his peak and hasn’t written anything as good as that one.