This state, in which nothing definite is thought, planned, striven for, desired or expected, which aims in no particular direction and yet knows itself capable alike of the possible and the impossible, so unswerving is its power -- this state, which is at bottom purposeless and egoless, was called ... truly "spiritual." It is in fact charged with spiritual awareness and is therefore also called "right presence of mind." This means that the mind or spirit is present everywhere, because it is nowhere attached to any particular place. And it can remain present because, even when related to this or that object, it does not cling to it by reflection and thus lose its original mobility. Like water filling a pond, which is always ready to flow off again, it can work its inexhaustible power because it is free, and be open to everything because it is empty. This state is essentially a primorial state, and its symbol, the empty circle, is not empty of meaning for him who stands within it.
Eugen Herrigel in Zen in the Art of Archery