Leonardo compares learning without genuine interest to eating without appetite or care. His point is that study is not simply a matter of taking in information. If the learner has little curiosity or engagement, the material may be received superficially and fail to become part of lasting memory.

The comparison also suggests a distinction between exposure to knowledge and meaningful understanding. Reading or studying can produce little benefit when it becomes mechanical, because attention and interest help organise new information and connect it with what is already known. The quote therefore presents learning as an active process rather than passive accumulation.

In practical terms, the passage can be read as an argument for purposeful study. It does not imply that every subject must be immediately enjoyable, but it stresses the importance of developing attention, curiosity and a reason for learning if knowledge is to be retained and used.