According to his widow Janet Asimov (in her biography of Isaac, It's Been a Good Life), he had no idea how to continue after Foundation and Earth, so he started writing the prequels.
Prema riječima njegove udovice Janet Asimov (u njezinoj biografiji Isaaca Asimova pod naslovom Bio je to dobar život/It's Been a Good Life), Asimov nije znao kako nastaviti nakon Zaklade i Zemlje, pa je stoga počeo pisati prequele ("prethotke").