“Success is the sum of small efforts, repeated day in and day out” is frequently—and incorrectly—credited to American self-help author Robert Collier (1885-1950). Collier’s book The Magic Word stated that the poetic lines came from Florence Taylor. The full verses (cited in print since at least 1932) are:
 
Success is the sum of small efforts,
Repeated day in and day out,
With never a thought of frustration,
With never a moment of doubt.
Whatever your cherished ambition,
Begin now to make it come true,
Through efforts, repeated, untiring,
Plus faith in the thing that you do.
 
   
Wikipedia: Robert Collier (author)
Robert Collier (April 19, 1885 in St. Louis, Missouri – 1950) was an American author of self-help, and New Thought metaphysical books in the 20th century. He was the nephew of Peter Fenelon Collier, founder of Collier’s Weekly. He was involved in writing, editing, and research for most of his life. His book The Secret of the Ages (1926) sold over 300,000 copies during his life. Collier wrote about the practical psychology of abundance, desire, faith, visualization, confident action, and becoming your best.
(...)
Quotes
. “Success is the sum of small efforts, repeated day in and day out.”
     
Google Books
Gleanings of Many Years of Discriminate Reading for My Own Use:
Together with Expressions of My Thoughts and Ideas, Herein Woven Together for Whatever Benefit They Might be to Others, Volume 2
By Andrew Mizell Burton
Nashville, TN: Williams Printing Company
1932
Pg. 188:
Success is the sum of small efforts,
Repeated day in and day out,
With never a thought of frustration,
With never a moment of doubt.
Whatever your cherished ambition,
Begin now to make it come true,
Through efforts, repeated, untiring,
Plus faith in the thing that you do.
 
19 October 1932, The Wyoming Post-Herald (Wyoming, IL), “The Wy-Hi Booster,” pg. 4, col. 1:
SUCCESS
Success is the sum of small efforts,
Repeated day in and day out,
With never a thought of frustration,
With never a moment of doubt.
Whatever your cherished ambition,
Begin now to make it come true,
Through efforts, repeated, untiring,
Plus faith in the thing that you do.
 
10 October 1938, Sikeston (MO) Herald, pg. 10, col. 5 ad:
SUCCESS
SUCCESS is the sum of small efforts,
Repeated day in and day out,
With never a thought of frustration,
With never a moment of doubt.
Whatever your cherished ambition,
Begin now to make it come true,
Through efforts, repeated, untiring,
Plus faith in the thing that you do.
—F. T.
(Super Success Hi-Test Gas.—ed.)
 
16 December 1939, The Daily Gleaner (Kingston, Jamaica), “Reflections,” pg. 44, col. 2:
Success is the sum of small efforts,
Repeated day in and day out,
With never a thought of frustration,
With never a moment of doubt;
Whatever your cherished ambition,
Begin now to make it come true,
Through efforts repeated untiring,
Plus faith in the thing that you can do.
FLORENCE WHITELY
Sent by Ouida Fay V. Buckley, Grange Hill.
 
2 December 1979, Corbin (KY) Times-Tribune, “Mountain Muse,” pg. 16, col. 7:
Success
Success is the sum of small efforts,
Repeated day in and day out,
With never a thought of frustration,
With never a moment of doubt.
Whatever your cherished ambition,
Begin now to make it come true,
Through efforts repeated untiring,
Plus faith in the thing that you do.
By NINA FLOYD
 
Google Books
The Magic Word
By Robert Collier
Lanham, MD: Start Publishing
2013
Pg. ?:
As Florence Taylor so aptly put it:
 
Success is the sum of small efforts,
Repeated day in and day out,
With never a thought of frustration,
With never a moment of doubt.
Whatever your cherished ambition,
Begin now to make it come true,
Through efforts, repeated, untiring,
Plus faith in the thing that you do.
 
Twitter
Quote Soup
‏@Quote_Soup
Success is the sum of small efforts, repeated day in and day out. - Robert Collier
11:41 PM - 11 Dec 2014