A person who thinks all the time,
has nothing to think about except thoughts.
So, he loses touch with reality,
and lives in the world of illusions by thoughts.
I mean specifically chatter in the the skull,
perpetual and compulsive repetition of
words of reckoning and calculating.

I am not saying that thinking is bad,
like everything else is useful in moderation,
a good servant but a bad master.
And all so-called civilised people have
increasingly become crazy and self destructive because
through excessive thinking they loses touch of reality.

That's to say we confused signs, words, number, symbols and ideas with real world.

-Alan Watts