[1] The expression is used also as an admission of having made a mistake that should have been avoided and, in a religious context, may be accompanied by symbolically beating the breast when uttering the words.
The phrase comes from a Western Christian prayer of confession of sinfulness, known as the Confiteor, used in the Roman Rite at the beginning of Mass or when receiving the sacrament of Penance.
Ideo precor beátam Maríam semper vírginem, omnes angelos et sanctos, et vos, fratres, oráre pro me ad Dóminum Deum nostrum.
Geoffrey Chaucer's 14th-century Troilus and Criseyde uses it in a way that shows it was already a traditional religious phrase: "Now, mea culpa, lord!
[5] In about 1220, the rite of public penance in Siena for those who had committed murder required the penitent to throw himself on the ground three times, saying: Mea culpa; peccavi; Domine miserere mei ("Through my fault.