Hillman's acorn theory, exposed in this book, is a rejuvenation of Heraclitus' dictum "ethos anthropoi daimon" (normally rendered into "Character is fate") and its later embodiments, such as Plato's myth of the daimon calling for a body to incarnate
after passing through the hands of the Fates and Necessity, Plotinus' postillae and commentaries, Romans' "homo faber fortunae suae", Ficino's ideas on souls, and so on and on. The echo of the oraculus of Apollo ("know yourself") lives on and inspires again the sensible reader of this famous work by the founder of the Archetypal psychology (as a follower of C. G. Jung).
Hillman indeed goes back to the myths as self-contained (bootstrapped) explanation of aspects of reality, and calls to re-install the right place and importance of the invisibles in human life after the rough blinding (that is, overflowing its original context) due to the Enlightment. So the book carries an atmosphere of fable and romanticism as it tells of genius, daimon, soul, angel and other wordly names of that acorn that may reside at the core of each person's life, thereby containing all further blossomings in a nutshell. Happyness as eudaimonia (assolving the requests of the daimon), fate and necessity, accidents to help the daimon express its power to give direction and an impelling sense of urgence and importance though without exceeding into the extremist position of fatalism and consequent de-responsabilization.
Hillman criticizes the current psychology's exclusive accent on "parental fallacy", genetical and environmental factors as all-inclusive explanations for children's future and achievements, and offers the daimon as a third way, besides nature and nurture, to explain the proper and unquestionably irreproducible development of the individual lives.
Hillman produces a large number of pieces of eminent biographies (and also discusses the often observed repulsion of relevant characters to encapsule their lives into biographies) to support his claims, considering the extraordinary as general case containing the ordinary as special. His style is soft and eloquent throughout, well spoken and passionate at times, devoid of technicisms but rich in images and facts.
Overall, this essay can be very stimulating in its provocative (yet old) claim, as it is provocative in calling for a return to older positions re-invented in hindsight and sub specie aeternitatis.