撞大运 (zhuàng dà yùn)

Try one’s luck; blind luck.

例：买彩票绝对是撞大运，所以，不要把它当回事，只是玩玩罢了。

(mǎi cǎi piào jué duì shì zhuàng dà yùn, suǒ yǐ, bú yào bǎ tā dāng huí shì, zhǐ shì wán wán bà le)

Playing the lottery is based absolutely on blind luck. So don’t take it seriously. You just play it for fun.