The Elder said to the brother: My son, the guardian of the eye is neither fear, nor aversion, nor flight, for these are weak servants that grow tired quickly. The guardian of the eye is discernment. It does not close the gate, but keeps watch over it, it does not make you blind, but teaches you where to look and how long to look. When discernment stands at the gate, the eye no longer clings to things, but passes through them as through a clean window, and then the heart remains free. Know this, my son: it is not the eye that sees purely, but the mind that has learned to choose, and the mind learns to choose only when it humbles itself. Then the Elder added: When the guardian sleeps, the eye wanders and when the guardian keeps watch, the eye becomes light.
Apophthegm
A brother said to the Elder: Father, how can I acquire discernment if I do not have it?
The Elder replied: Begin by not trusting yourself.
The brother was troubled and said within himself: How can I walk if I do not lean on myself?
Pustia Inimii 