What you are, you are by accident of birth; what I am, I am by myself. There are and will be a thousand princes; there is only one Beethoven.
Ludwig van Beethoven
I like that one a lot, especially when one imagines in what times the statement was made. Two other Beethoven quotes - mind my possibly poor translation from German.
"In these days I did not know how to compose. Nowadays, I think, I know it" (response to an admirer of his septet op.20)
A very deliberate and self-consciousnes statement, apparently made in the context of op. 106:
The limits are not yet drawn which oppose talent and perseverance and which might declare "only until here and no further".
There is one Liszt quote I also like a lot:
My piano is for me what the fregate for the seafarer, the horse for the Arab -- no, it is more than that, as it has been my self, my language, my life.
(Mein Klavier ist für mich, was dem Seemann seine Fregatte, dem Araber sein Pferd -- mehr noch, es war ja bis jetzt mein Ich, meine Sprache, mein Leben.)