The approach
One dominant source, placed high and slightly off axis, with the fall-off allowed to run deep. Nothing lifting the shadow side beyond what was needed to keep detail in the cloth. The method is Caravaggio's and I make no apology for saying so plainly: light from one direction, darkness permitted to remain dark, and the face emerging rather than presented.
The reason it suits a mind like this is that it removes almost everything. There is no environment to read, no desk, no bookshelf standing in for authority. What is left is bone structure and attention.