Unknown author · Public domain

Lev Vygotsky argued that a child's mind is not simply hard-wired but built through language, tools, and other people — the gap between what a child can do alone and what they can do with guidance, his "zone of proximal development," remains one of the most cited ideas in developmental psychology. He died of tuberculosis at 37, having written most of his major work in the last decade of his life; Stalin then had his books banned, and they weren't published as a collection until 1956, two decades after his death.