"The state of photography nowadays is such that the amateur and professional alike are surrounded by an overwhelming mass of all kinds of materials — cameras, plates, films, papers, chemicals — with the inevitable result that any one individual who does not succeed with a certain class of goods will prefer to leave it and try another, rather than try to ascertain the reasons for his failure.  It is not enough, furthermore, to be satisfied if we are successful; let us endeavour to find out why success has attended our efforts, every bit as much as failure, so that a clear knowledge of the principles of photography shall guide our future work, and make us as independent as possible of facts, formulae, and friends."

Successful Negative Making, 2nd Edition, by T.Thorne Baker, 1905.

"August 8, 1930
I could wait no longer to print them — my new peppers, so I put aside several orders, and yesterday afternoon had an exciting time with seven negatives.

First I printed my favorite, the one made last Saturday, August 2, just as the light was failing — quickly made, but with a week's previous effort back of my immediate unhesitating decision.  A week? — yes, on this certain pepper — but twenty years of effort starting with a youth on a farm in Michigan, armed with a No. 2 Bull's Eye Kodak, 3½ x 3½, have gone into the making of this pepper, which I consider a peak of achievement."

Edward Weston  The Flame of Recognition, edited by Nancy Newhall, 1975.

Boyden, E. S. "How to Think." Ed Boyden's Blog. Technology Review. 11/13/07. http://www.technologyreview.com/blog/boyden/21925/.
An invaluable summary of the scientific/artistic process.