A man must dream a long time in order to act with grandeur, and dreaming is nursed in darkness.

Greatness of action, Genet suggests, is not improvised. It is the visible end of a long, hidden rehearsal in the imagination, and that rehearsal happens out of sight, in a place where no one is judging. Darkness here means privacy, obscurity and even humiliation, the conditions in which a person can imagine freely because nobody is watching. It's easy to see why this idea mattered to him. Genet grew up as a foster child, became a petty thief, and spent time in prison, where he began writing. His books turn exclusion and shame into something grand, and that transformation had to be dreamed first, in confinement, before it could become literature.

The thought also echoes older Romantic and Symbolist ideas that the inner life is where values and visions are formed, long before they show up in deeds. Dreaming isn't an escape from action. It's the slow preparation for it.

A modern version might be someone who wants to change careers or write a first book. Instead of rushing to announce it, they protect a few quiet evenings a week to imagine it in detail, sketching scenes or picturing the work they'd like to do, without needing to show results. When they finally act, the action has weight because it was lived inwardly first.