“Any act often repeated soon forms a habit : and habit allowed, steadily gains in strength. — At first it may be but as the spider’s web, easily broken through, but if not resisted it soon binds us with chains of steel.”

Source: The Summing Up (1938), p. 182

Vol. I, ch. 10
Lady Holland's Memoir (1855)

Though Buffet is reported to have expressed such ideas with such remarks many times in his lectures, he never claimed to originate the idea, and in the article "The Chains of Habit Are Too Light To Be Felt Until They Are Too Heavy To Be Broken" at the Quote Investigator http://quoteinvestigator.com/tag/warren-buffett/ it is shown that this sort of expression about chains goes back at least to similar ideas presented by Samuel Johnson in "The Vision of Theodore, The Hermit of Teneriffe, Found in His Cell" in The Gentleman’s Magazine, Vol. 18 (April 1748), p.160:
It was the peculiar artifice of Habit not to suffer her power to be felt at first. Those whom she led, she had the address of appearing only to attend, but was continually doubling her chains upon her companions; which were so slender in themselves, and so silently fastened, that while the attention was engaged by other objects, they were not easily perceived. Each link grew tighter as it had been longer worn, and when, by continual additions, they became so heavy as to be felt, they were very frequently too strong to be broken.
Such sentiments were later succinctly summarized by Maria Edgeworth in Moral Tales For Young People by Miss Edgeworth (1806), Vol 1, Second Edition, p. 86:
… the diminutive chains of habit, as somebody says, are scarcely ever heavy enough to be felt, till they are too strong to be broken.
Disputed

Heath's book of Beauty, 1833 (1832)

Las cadenas que más nos encadenan son las cadenas que hemos roto.
Voces (1943)

1951 - 1968, Apropos of Ready Mades', 1961

Source: Dictionary of Burning Words of Brilliant Writers (1895), P. 296.