It's not so much training as evolved instinct. The extent to which "training" is involved is simply a lack of training to combat this instinct.
Our ancestors had a survival benefit to treating their own bodies as distinct from the rest of the universe. Prioritizing damage avoidance for parts of one's own body over the rest of the universe was a strategy that improved individual survival chances.
Our instinctive perceptions were shaped by survival benefit, not quintessential truth.
@isaackuo @skye That is true, but it's also true that esp. western tradition has exacerbated this, by attempting to apply atomism to everything.
Atomism (before instrumentation to actually detect atoms) engenders an analytical approach, dissecting things into parts that can be "nailed down" and called fundamental.
But it breaks down completely if an investigator tries to turn that scalpel on themselves.
So, in favoring "what works", most traditions simply avoided going to where it all unravels.
I also think this is analogous to how people felt strongly that there is a soul, because they feel like they are "living inside" their bodies, and could not envision that the body (which can be dissected and "nailed down") could possibly have anything to do with the ineffable mind. Hence the mind must be part of something indissectible.
Isaac Ji Kuo
Androcat