a soul-tragedy of no mean proportion

What does the part in bold mean?

In one authorial interruption, Robins
generalizes about the experience of a woman writer in her
day: Who shall not say there was no element of courage and
of steadfast strength in the woman who, year in, year out,
sat chained to her writing-table, ceaselessly commemorating
the futile and inept, leaving behind her day by day
upon that sacrificial altar some fragment of youth and
health, some shred of hope, some dead illusion. To sit
down daily to the task of being George Eliot, and to rise
up "the average lady-novelist" to the end, must, even if
only dimly comprehended, be a soul-tragedy of no mean
proportion.

— Elaine Showalter, A Literature of Their Own: British Women Novelists from Bronte to Lessing, 2020