Cookies

Why do I have to say NO 15 hundred times? And what's with the selective hearing?

For example: 

"More cookies?" 

"No."

"More cookies!"

"No. Do you want an apple?"

"MORE COOKIES!!!" (reaching for cookies)

"No."

"MOOOORE COOOOOKIEEEEES!!!" (still reaching for cookies)

"No."

(Crying ensues....)

Why do I have to say no 15 billion times before he accepts that the answer is No? And why does he act like he doesn't hear what I am saying and continues to reach for the cookies?

All rhetorical questions, of course. For the answer, we all know, and my husband reminds me of often, is "Because he is 2."