I personally am fond of the epigraphs in Zettl, Anton. Sturm-liouville theory. No. 121. American Mathematical Soc., 2010. Here are a selected few:

(Chapter 10: Singular Self-Adjoint Operators)
One can measure the importance of a scientific work by the number of earlier publications rendered superfluous by it.
In H. Eves Mathematical Circles Revisted, Boston: Prindle, Weber and Schmidt, 1971

Mathematics knows no races or geographic boundaries; for mathematics, the cultural world is one country
In H. Eves Mathematical Circles Revisted, Boston: Prindle, Weber and Schmidt, 1971

$ $

(Chapter 11: Singular Indefinite problems)
Biographical history, as taught by public schools, is still largely a history of boneheads: ridiculous kings and queens, paranoid political leaders, compulsive voyagers, ignorant generals - the flotsam and jetsam of historical currents. The men who radically altered history, the great scientists and mathematicians are seldom mentioned, if at all.
Martin Gardner

$ $

(Chapter 13: Two Intervals)
Each problem I solved became a rule which served afterwards to solve other problems.
Renee Descartes

I personally am fond of the epigraphs in Zettl, Anton. Sturm-liouville theory. No. 121. American Mathematical Soc., 2010. Here are a selected few:

(Chapter 10: Singular Self-Adjoint Operators)
One can measure the importance of a scientific work by the number of earlier publications rendered superfluous by it.
In H. Eves Mathematical Circles Revisted, Boston: Prindle, Weber and Schmidt, 1971

Mathematics knows no races or geographic boundaries; for mathematics, the cultural world is one country
In H. Eves Mathematical Circles Revisted, Boston: Prindle, Weber and Schmidt, 1971

$ $

(Chapter 11: Singular Indefinite problems)
Biographical history, as taught by public schools, is still largely a history of boneheads: ridiculous kings and queens, paranoid political leaders, compulsive voyagers, ignorant generals - the flotsam and jetsam of historical currents. The men who radically altered history, the great scientists and mathematicians are seldom mentioned, if at all.
Martin Gardner

$ $

(Chapter 13: Two Intervals)
Each problem I solved became a rule which served afterwards to solve other problems.
René Descartes