In one sentence, enlightenment is man's emergence from his self-incurred immaturity.
What is immaturity? "Immaturity is the inability to use one's own understanding without the guidance of another." If someone doesn't have the courage to use his or her understanding, in that case, the immaturity is self-incured.
The motto of enlightenment is therefore: Sapere aude! Have courage to use your own understanding!
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