你又不是太阳怎么会发光
[nĭ yòu bù shì tài yáng zĕn me huì fā guāng]
The literal translation is 'You’re not the sun, so how can you shine?'. It implies that a person might be boasting or showing off excessively, to the point where it’s unrealistic for them to match up to something as extraordinary as the sun.