We will learn how. It is simple.
despite the fact that if we think life is "an illusion, and all experiences of other people are justly the same illusion, rendering all their testimonies and experiences fallible evidence",
we can determine that reality is not an illusion because it still exists. Whether perceived as an illusion or not, you factually alter it and react with it. Therefor, the substance of the "illusion" is positively effected or negatively effected by you, and those reactions are real, so it is too.
Life, by definition is not an illusion, because an illusion is something which does not correlate with material law.
fact. This argument resolves the theological question.