What is Advaita?
It is not possible to say that Brahman and the Atman are one because in the Advaita experience the ego dissolves. Without the ego there is no one left to do the counting.
In that state a man no longer finds the existence of his ego. And who is there left to seek it? Who can describe how he feels in that state - in his own Pure Consciousness - about the real nature of Brahman? There is a sign of Perfect Knowledge. Man becomes silent when It is attained. Then the 'I', which may be likened to the salt doll, melts in the ocean of Existence-Knowledge-Bliss Absolute and becomes one with It. Not the slightest distinction is left.
The Gospel of Sri Ramakrishna, The Master with the Brahmo Devotees (I), October 28, 1882
Note: “The question: What is Advaita?” is licensed by Stack Exchange Inc (https://hinduism.stackexchange.com/); user contributions licensed under CC BY-SA.