Leonardo uses the physical properties of clay as a metaphor for the capacity to change. Before clay is fired, it remains flexible enough to be reshaped even after damage. Once it has been baked, however, its form is fixed and breaking it cannot be reversed by simply moulding it again.

Applied to human behaviour, the comparison suggests that attitudes, habits and aspects of character may be easier to alter while they are still developing. Repeated behaviour and long-established patterns can become more resistant to change, just as firing transforms soft clay into a rigid material.

The quote can therefore be applied to education, personal development and habit formation. It emphasises the value of addressing problems while change remains relatively easy. It does not imply that people eventually become incapable of change, but it highlights how established patterns can require substantially greater effort to reshape.