The present research is based on material from Old Russian lives of holy fools: Isaacius of the Cave Monastery, Procopius and John of Ustyug, Basil the Blessed, John Bolshoy Kolpak (Big Cap), Simon of Yuryevets, John Vlasaty (the Hairy), Maximus of Totma, Procopius of Vyatka, John Samsonovich of Solvychegodsk, Artemius Tretyak, and others. The main ascetic motifs that determine this type of hagiographic texts are examined in the context of hagiographic topoi. Many ascetic motifs of the lives of holy fools, which is an element of the system of hagiographic topoi, demonstrate kinship with ascetic motifs of the lives of holy monks (e.g., severe fasting, wearing chains, suffering from cold and heat, etc.), and in some cases also with the lives of martyrs (e.g., fire motifs). At the same time, some ascetic practices described in the lives of holy fools are rather provocative (nudity or aggressive behavior) or take place in a veiled form (e.g., hidden fasts) in accordance with an emphasis on the unusual feat for the sake of Christ. The aim of this feat was to hide one’s virtues. A focus on examples, which is one of the essential elements of the structure of hagiographic texts generally and of the lives of holy fools in particular, reflects a historical continuity of the extreme feat as such. The explanation of this cultural phenomenon could lie in the fact that Old Russian hagiographers, as well as their heroes, followed the most important ethical and aesthetic guideline of their time—the principle of imitatio, which to a great extent determined literary and behavioral strategies of the Middle Ages.