This book is the first exploration of an essential theme in the thought of the 7th c. East-Syriac solitary and mystic Isaac of Nineveh, that of creatural "weakness" (mihiluta), a term which, in Isaac, alludes to the ontological condition of exposure to limitation and suffering that characterizes all humans. Based on the analysis of Isaac's edited and unedited writings in the original Syriac, the book sheds light on his understanding of creatural vulnerability and the phenomenology of the relationship with vulnerability that he outlines, with references to the authors who influenced him (Evagrius, the Syriac Pseudo-Macarian corpus, and others). The reader is thus introduced to Isaac's view of human finitude which, if experienced and "inhabited", can be taken on by the subject and disclose an experience of integrity. The solitary life, in this perspective, involves entering the mystery of suffering that marks every creatural life.