Herzl did not speak Hebrew. He wrote 'Im tirtzu...' (fully 'im tirtzu, ein zo agada; ve'im lo tirtzu, agada hi ve'agada tisha'er', אם תרצו, אין זו אגדה; ואם לא תרצו, אגדה היא ואגדה תישאר, meaning, 'If you will it, it is no dream; and if you do not will it, a dream it is and a dream it will stay).
In Altneuland, which is credited as the source for this quote, Herzl said "If you do not will it, it is only a fairy tale". Nowhere did it say in the book, however, that it would not be a fairy tale if you will it. The converse of a statement is not necessarily true. So I am not sure whether this converse that is often quoted is something Herzl actually said or if it was just a later interpretation of his words. Will someone please explain.