In fact, in May of last year, Duterte explained his decision by recounting a conversation he had with Xi Jinping a year earlier, in which Xi threatened war:

Duterte: Mr. Xi Jinping, I will insist that it is ours and we will drill oil. [T]hat is ours and we intend to drill oil there. My view is I can drill the oil.
（习先生，我们要钻油，因为那里是我们的）

Xi: Well we are friends. We don’t want to quarrel with you. We want to maintain warm relationship, but if you force the issue we will go to war.
（我们是朋友，我不想和你吵架，但是那里是我们，你要钻油，那就意味着战争）

Duterte: I’ll drill the oil. （我就是要钻，就钻，就钻。。）

Xi: Please do not do that because that is ours. （劝你别那么干，那是我们的）

Duterte: That is according to you. But I have the arbitral [referring to the Hague tribunal ruling].
（那是你这么说，人家法院都说是我们的）

Xi: Yes, but ours is historical and yours is legal of recent memory.
（但是历史上是我们的）

Duterte: But that’s too far away. It’s almost alien to us to hear those words because we were never under Chinese jurisdiction.
（那也太久远了吧？？我听着跟天书一样，我们无法理解中国人的裁判）

Xi: Well, if you force the issue, we’ll be forced to tell you the truth.
（如果你非要干，那么我只好告诉你实话了）

Duterte: So what is the truth? （啥？）

Xi: We will go to war. We will fight you.
（我们和你们打仗）


（老杜说，要打仗，那就是等于对我们的屠杀，还是拉倒吧）