Mark Twain's statement offers a fascinating perspective on language acquisition and understanding. The emphasis on knowing grammar by ear rather than by explicit rules or notes underscores the natural and intuitive aspect of language. This suggests that true mastery of language often comes through immersion and experience rather than rote memorization or formal instruction alone.

From a broader perspective, this quote reflects the important distinction between theoretical knowledge and practical application. Grammar rules can be learned from books, but the subtle nuances and rhythms of language are best absorbed through listening, speaking, and engaging in communication. It highlights the value of practical exposure in internalizing linguistic patterns, which enables fluid and natural use of language.

Moreover, Twain's insight encourages us to appreciate the organic nature of human language and cognition, which often thrives outside rigid systems. It subtly critiques an overly prescriptive or academic approach to grammar that might stifle language's dynamic and evolving character. This approach is particularly relevant in language learning; a balance between understanding grammar rules and developing an intuitive feel for the language is essential for genuine fluency.

Ultimately, this quote reminds us to trust our ears and experiences and underscores the mystery of how the human brain effortlessly acquires and processes complex linguistic structures without conscious rule-following. It celebrates an innate capacity for language that goes beyond formal education, urging learners and educators to value immersive and experiential methods.