yuē rén qián xiān kàn hái yǒuméiyǒu piào, bùrán shíjiān dìng hǎo le, què fāxiàn yùyuē mǎn le

约人前先看还有没有票，不然时间定好了，却发现预约满了。

Check if there are still tickets before asking someone out, otherwise you might set a time only to find that it is fully booked