3-minute passion is a Chinese saying which refers to a person having a limited passion or a passion that doesn't last long toward something/someone that he/she liked/loved/had passion about. 

“三分钟热度”是个中国俗语，指的是一个人对他喜欢、或者有热情的人或事物只能保持有限或短暂的热情。

例句：

 A: I would like to learn piano therefore I will need to buy one. 

B: Oh, I suggest that you think carefully before you buy one as you are always a '3-minute passion' person. 

A：我想学钢琴，所以得买一架。 

B：哦，我建议你买之前要仔细考虑，因为你经常只有三分钟热度。