Things might have been
Summer dreamstate
Sure of itself
The conditions of experience explain why objects appear to have particular properties. Thus appearances are epistemologically fundamental to explaining experience. Philosophical theorizing about perception also involves the observation that things are not always as they appear. Of course, an experienced illusion is a specific manifestation and in this regard illusions exist.
“The universal reality of all relative existence is something else; therefore, it is like an illusion.” – Thubten Yeshe