Was perhaps from the moment that Monsterkind were hurled down Mt Ebott like trash that W.D. Gaster knew humans were rotten creatures? Or maybe it was instead during the war when he had been but a young child. Forced to flee from all he's ever known as battle raged across lands, then later as he grew up to create weapons of mass destruction. Perhaps, it was before he was even born that he had know this truth. Gaster was, after all, one of the smartest monsters to have ever lived, and most certainly was the smartest monster in the Underground. Because humans were dangerous, after all. They were miserable, miserable creatures that were powerful yes, but miserable. And his next invention would be the bridge to that gap between their two races. No. Rather then gap it was a chasm. He would create the first biological weapon, and once the barrier was destroyed then nothing would get in its way.