The best and most beautiful things in the world cannot be seen or even touched — they must be felt with the heart.

Helen Keller (1880-1968) American author and lecturer
The Story of My Life (1905)

The above is the popular paraphrase. The text as in the book was from  a letter from Keller to Rev. Phillips Brooks (8 Jun 1891), which attributed the original thought to her teacher, Anne Sullivan:

I used to wish that I could see pictures with my hands as I do statues, but now I do not often think about it because my dear Father has filled my mind with beautiful pictures, even of things I cannot see. If the light were not in your eyes, dear Mr. Brooks, you would understand better how happy your little Helen was when her teacher explained to her that the best and most beautiful things in the world cannot be seen nor even touched, but just felt in the heart. Every day I find out something which makes me glad.

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