憑什麼的英文?

U may say :

ON WHAT GROUNDS do you think I should do what you say ?

GROUNDS
def : reasons, especially that makes you think that something is true or correct.

eg : Leo has strong GROUNDS for asking for more money.
eg : He refused to sign the contract on moral GROUNDS.
eg : Fiona was awarded compensation on the GROUNDS that the doctor had been negligent.

憑乜野要我照你既說話去做?

Give me a good reason why should I do as you said?

憑乜野要我照你既說話去做:
Depends on to glance sideways wildly wants me
already to speak according to you does

Why i use to follow what you said?