In Hua-yan, ultimate truth is “inconceivable” because it is beyond the limitations of language (everyday phenomena of mental projections).
Ultimate reality is simply the way things are. For this reason, we use the term “thusness” to describe them. They are just what they are.
Thusness means the way things are on their own, beyond our mental projections.
Things are actually all identical, but when we attempt to describe them (with our thoughts and language), then we make them different from each other through out minds.