Arnold Böcklin (1827 - 1901), the 19th century artist famous for his canvases of centaurs and mermaids, once said,
“Nothing in art is created without effort, and the painter’s ideas don’t come to him on wings while he dreams, either. The one may be more talented than the other, of course; but without untiring diligence, single-mindedness and a combative spirit, there can’t be any good result. All this talk about ‘inspiration’ is nonsense.”
Musee d'Orsay article about him, link.