The greatest lesson I ever learned was the cheerful destruction of a false start. Don't be afraid of your eraser: use it all the time & keep it always handy, & don't ever go ahead on a picture till the drawing of it satisfies you fully. If necessary, carry it farther then you need for an outline merely, -suggest shading enough to show if it is going to "solidify" right, & then erase the shading before painting. But a thing falsely drawn will never prove up, & you'll waste a heap of time, trying to convince yourself you're righting a wrong. Better by far to build well, as you go along, and remove every fault as it comes. That is progress, and the results will show immediately.

-Louis Agassiz Fuertes in a letter to George Miksch Sutton from To a Young Bird Artist