Bob Schwartz

Une difficulté est une lumière. Une difficulté insurmontable est un soleil: ‘A difficulty is a light. An insurmountable difficulty is a sun.’
Paul Valéry

From the Introduction to The History of Philosophy by A.C. Grayling:

But the core of questions in epistemology, metaphysics, ethics, political philosophy, the ‘philosophy of’ pursuits, and the rest, remain; they are perennial and perennially urgent questions, because efforts to answer them are part of the great adventure of humanity’s effort to understand itself and its place in the universe. Some of those questions seem unanswerable – though to act on the thought that they are so is to give up far too soon. Moreover, as Paul Valéry said, Une difficulté est une lumière. Une difficulté insurmontable est un soleil: ‘A difficulty is a light. An insurmountable difficulty is a sun.’ Wonderful saying! for it teaches us that the effort to solve even the seemingly unsolvable teaches us an enormous amount – as the history of philosophy attests.