Chiaroscuro is the rendering of the lights and the darks in a painting. How this is done depends partly upon the particular style of the artist but, regardless of style, a certain amount of technical skill is still necessary for a satisfactory result to be achieved.
Quite often, a beginning artist will fail to achieve sufficient contrast between the lights and the darks of a painting. I suspect this happens when the artist sees success in sight and becomes afraid to do anything which may ruin his or her creation. It does take confidence to boldly intensify the darks with, sometimes, heavy pressure and to lighten (or lift) the lights, by erasing previously rendered sections of work. But, without this final stage, the picture will look somewhat flat and insipid.
I, also, find my confidence dipping at this crucial stage, particularly when I have achieved a pleasing likeness and I am reluctant to spoil that likeness with further tampering. But, success in art depends on taking risks, whether the artist paints in an abstract, contemporary or realistic style. With risking-taking comes growth, and growth produces increasing levels of success, sometimes success which is far beyond the artist's original expectations.
The other extreme in art is knowing when to stop. This is a skill which comes naturally to some artists and which others have to acquire. Here, too, I find that I have to be very strict with myself as an overworked picture can look clumsy, muddy or overcomplicated. The number of times my family have had to force me to call it a day are too numerous to count! Probably, this stems from perfectionism - a trait which is all too common whenever anyone takes a pride or personal satisfaction in their creative activities.
In this picture, I have yet to complete my final tonal values. Though the tones are near completion on the work so far, the final darkening of the darks and lifting of the lights will make a significant difference to the end result.