Within experience, people seem to have a very real sense of being a separate thing, distinct from the rest of the universe.
And it seems like this experience is supported by what we can sense of the relationship between the physical ‘us’ and the rest of physical reality.
But what if a really close look at the relationship between these two parts of physical reality showed that their apparent separateness was an illusion?
That would mean that of the two apparent certainties supporting our sense of separateness (conscious experience and the evidence of physical reality), one would be removed.
And any thought that it might have scientific support would go with it.
In fact it would create a paradoxical situation where the scientific evidence indicated a lack of separation between the physical body and Universe, while “Common sense”, “Self evident” interpretation of conscious experience would indicate the exact opposite.
And since the science were sufficiently settled (that we are fully a process of the universe), then the only place left open to question would be within our personal interpretation of conscious experience.