Le Violon d'Ingres

As a young man, the French neo-classic painter Jean Auguste Dominique Ingres (1780-1867) was often strapped for money. He played the violin somewhat; as a teenager he was a second violinist in the Orchestre du Capitole de Toulouse. When Ingres needed cash to buy paints, often it was his violin playing which would solve the problem. The expression "Le Violon d'Ingres"--Ingres' Violin--came to mean something you had to do in order to do something you wanted to do.