To be human is to be always in relation to others. Vygotsky emphasizes the centrality of social interaction in cognitive development. Even the self-directed learning of the autodidact is tied to a social context. Vygotsky (1978: 57) asserts that:

Every function in the child's cultural development appears twice: first, on the social level, and later, on the individual level; first, between people (interpsychological) and then inside the child (intrapsychological). This applies equally to voluntary attention, to logical memory, and to the formation of concepts. All the higher functions originate as actual relationships between individuals.

Vygotsky’s Zone of Proximal Development was entirely social. His original notion of the ZPD was revealed to academia in the West decades after he died. ZPD was defined (1978: 86) as the space between the:

actual developmental level as determined by independent problem solving and the level of potential development as determined through problem solving under adult guidance or in collaboration with more capable peers.

The ZPD concept invites scaffolding from the teacher or peers; which can be removed when it is no longer needed.

Vygotsky, L. S. (1978). Mind in society: The development of higher psychological processes. Cambridge, MA: Harvard University Press.