In his essay "On Liberty", John Stuart Mill stated that "human nature is not a machine, but a tree."
The quote follows as, “Human nature is not a machine to be built after a model and set to do exactly the work prescribed for it, but a tree, which requires to grow and develop itself on all sides, according to the tendency of the inward forces which make it a living thing.” He on individual freedom elucidates his concept.
The above line is quoted from chapter three wherein Mill discusses whether unpopular views held by the people should be allowed to act on them without facing legal penalty and being made social outcasts. Further discusses an outright nuisance and harm can be eradicated by implementing limited actions of the law. In addition, elaborating that the humans must need to experiment under different conditions of living as they are fallible. Therefore, in order to achieve personal and social progress, individual liberty must be expressed.