The factor which determines the course of this inner development is the material world with all its objective qualities, to which man must adapt himself in order to be able to utilize his own faculties freely.

Mario Montessori Jr, Education for Human Development

Inner forces affect his choices, and if someone usurps the function of this guide, the child is prevented from developing either his will or his concentration.

Maria Montessori, The Absorbent Mind

The child's nature is to aim directly and energetically at functional independence. A vital force is active within him, and this guides his efforts towards their goal.

Maria Montessori, The Absorbent Mind