it's obvious

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"Obvious" is a curious word. It is used to designate what is perceived or known.

But what is obvious to you may not be obvious to me and what is obvious to me may not be obvious to you.

And if this is the case, how "obvious" could anything be?

Maybe this explains why Zen teachers of the past sent their students sprawling -- smacked them silly -- and why Zen students, once they had gained their footing, did the same for their teachers.

Of course parents kiss their children good night for the same obvious reason.
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