..learn to draw: that's where most of you [Troyon's pupils] are falling down today.. ..draw with all your might; you can never learn to much. However, don't neglect painting, go to the country from time to time and make studies and above all develop them.

Notes from Wikiquote

Monet is quoting in his letter Troyon, who was a good friend of his first art-teacher Eugène Boudin in Le Havre