Meaning of “the strongest principle of growth lies in human…”

Gitanjali, poem 4, in Tagore’s own prose translations from Bengali; Project Gutenberg #7164. The omitted continuation explicitly attributes the strength to act to the divine addressee, so the line remains religious rather than generic productivity advice.

Moral printed after “Hercules and the Wagoner” in the Townsend translation; Hercules first tells the driver to help himself.

Latter-Day Pamphlets, No. IV “The New Downing Street”; Project Gutenberg #1140. The sentence occurs inside Carlyle’s controversial political argument about leadership; this collection uses it for work/responsibility while retaining that historical context.

Poor Richard’s Almanack.

Sartor Resartus, Book II, Chapter IX, “The Everlasting Yea,” printed page 156 / Wikisource scan leaf 188 in The Works of Thomas Carlyle, Centenary Edition, Vol. I (New York: Charles Scribner’s Sons, 1896). “Do the Duty which lies nearest thee” follows the doubt/action sentence and is explicitly described as a precept that was of invaluable service to Teufelsdröckh. It remains fictional-philosophical and religious conduct-of-life rhetoric rather than a context-free productivity command.

Human Nature and Conduct (1922), Part Four, Section III, “What is Freedom?”, printed page 304, Project Gutenberg #41386. Dewey states “Intelligence is the key to freedom in act” while arguing that effective action depends on consulting conditions and forming plans that enlist their cooperation; the following page stresses study, foresight and adaptation. This is historical philosophical / social-psychological argument rather than current neuroscientific or experimentally settled behavioral evidence.