There is a certain perfection in accident which we never consciously attain.
 Henry David Thoreau, A Week on the Concord and Merrimack Rivers (1849). copy citation

Context

“The unconsciousness of man is the consciousness of God. Deep are the foundations of sincerity. Even stone walls have their foundation below the frost. What is produced by a free stroke charms us, like the forms of lichens and leaves. There is a certain perfection in accident which we never consciously attain. Draw a blunt quill filled with ink over a sheet of paper, and fold the paper before the ink is dry, transversely to this line, and a delicately shaded and regular figure will be produced, in some respects more pleasing than an elaborate drawing.” source