Full Idea
Kant does not dictate what the maxim (the principle) of my action should be, and this is the crux. The individual has to decide the basis for their actions, rather than have it imposed on them, which differentiates us from the world of nature.
Gist of Idea
The maxim of an action is chosen, and not externally imposed
Source
report of Immanuel Kant (Groundwork of the Metaphysic of Morals [1785]) by Andrew Bowie - German Philosophy: a very short introduction 1
Book Reference
Bowie,Andrew: 'German Philosophy: very short intro' [OUP 2010], p.16
A Reaction
Apparenty this inspired the Romantic era (the Age of Freedom?) just as much as the French Revolution. It is the chief doctrine of extreme individualism - except that the maxim chosen should be one on which rational beings should agree.