This paper examines the Manuscript "Concrete Human Psychology", by Lev Vygotsky, with the purpose of highlighting the vigour of the author's arguments about the fundamental role of social relations in the individual formation. The focus lies on passages of the text which are more pertinent to the reciprocal construction of the "self" and the "other". In the approach to this theme, some propositions of Pierre Janet are explored, since he is one of the most important references (the) Vygotsky includes in the Manuscript. Next, the contributions of these self and the other, in the imaginary play of children. Finally, the proficuous perspectives for investigation offered by the Manuscript are remarked, as well as the complex issues that it leaves unclosed.