Self-knowledge is something that cannot be bought or easily acquired, much like a precious commodity that is rarely available for sale. The quote suggests that understanding oneself is a difficult journey that requires personal effort and insight, rather than material acquisition or external validation.
In essence, gaining true self-awareness is a challenging process that few are willing or able to undertake. Dorothy Dunnett implies that self-knowledge is valuable but elusive, highlighting its importance as an inner quest rather than a marketable item.