“It is above all things necessary to form a true estimate of oneself.”
A realistic estimate of one’s abilities and limits supports both confidence and humility, reducing the instability that comes from either self-contempt or exaggerated self-belief.
Source details
Of Peace of Mind, section VI, Aubrey Stewart translation (1889), cross-checked against Project Gutenberg #64576 and Wikisource. The sentence opens Seneca’s advice to form a true estimate of oneself before matching undertakings to one’s actual abilities and temperament.