"Even if a monk is not skilled in the ways of the minds of others, he should train himself: 'I will be skilled in reading my own mind.'
"And how is a monk skilled in reading his own mind?
Imagine a young woman, fond of adornment, examining the image of her own face in a bright, clean mirror :
If she saw any dirt or blemish there, she would try to remove it. If she saw no dirt or blemish there, she would be pleased, her resolves fulfilled: 'How fortunate I am! How clean I am!'
In the same way, a monk's self-examination is very productive in terms of skillful qualities [if he conducts it in this way]: 'Do I usually remain covetous or not? With thoughts of ill will or not? Overcome by sloth & drowsiness or not? Restless or not? Uncertain or gone beyond uncertainty? Angry or not? With soiled thoughts or unsoiled thoughts? With my body aroused or unaroused? Lazy or with persistence aroused? Unconcentrated or concentrated?'
Sacitta Sutta -One's Own Mind