Einstein sets two explanations of his work against each other and rejects the first. He does not claim to have been born with unusual ability; he claims only to have wanted to understand things, and to have kept wanting to.

The force of the sentence lies in the word “only”. Curiosity is offered as the smaller and more ordinary of the two explanations, and therefore as something available to anyone. Whether that account is complete is another matter, and readers may reasonably think he understates his abilities.

He wrote it in a letter of 11 March 1952 to Carl Seelig, who was then researching a biography of him. The German reads that he had no particular Begabung, meaning aptitude or gift. A year later he made a similar remark to Hans Muehsam, so it was a considered self-description rather than a passing modesty.

Original (in German)