“The chains of habit are too weak to be felt until they are too strong to be broken.”

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

pg 71
Source: The Unbearable Lightness of Being (1984), Part Two: Soul and Body

Letter IV
The Nemesis of Faith (1849)
Context: There is a village in the wood, two or three miles from here — there was an abbey there once. But there is nothing left of the abbey but its crumbling walls, and it serves only for a burying-ground and for sentimental picnic parties. I was there to-day; I sat there a long time, I do not know how long — I was not conscious of the place. I was listening to what it was saying to me. I will write it down and look at it, and you shall look at it: an odd enough subject for a Christian ruin to choose — it began to talk about paganism. "Do you know what paganism means? " it said. Pagani, Pagans, the old country villagers. In all history there is no more touching word than that one of Pagan.
'In the great cities, where men gather in their crowds and the work of the world is done, and the fate of the world is determined, there it is that the ideas of succeeding eras breed and grow and gather form and power, and grave out the moulds for the stamp of after ages. There it was, in those old Roman times, that the new faith rose in its strength, with its churches, its lecture-rooms, its societies. It threw down the gorgeous temples, it burnt their carved cedar work, it defiled the altars and scattered the ashes to the winds. The statues were sanctified and made the images of saints, the augurs' colleges were rudely violated, and they who were still faithful were offered up as martyrs, or scattered as wanderers over the face of the earth, and the old gods were expelled from their old dominion — the divinity of nature before the divinity of man. … Change is strong, but habit is strong too; and you cannot change the old for new, like a garment. Far out in the country, in the woods, in the villages, for a few more centuries, the deposed gods still found a refuge in the simple minds of simple men, who were contented to walk in the ways of their fathers — to believe where they had believed, to pray where they had prayed. What was it to these, the pomp of the gorgeous worship, the hierarchy of saints, the proud cathedral, and the thoughts which shook mankind? Did not the sky bend over them as of old in its calm beauty, the sun roll on the same old path, and give them light and warmth and happy sunny hearts? The star-gods still watched them as they slept — why should they turn away? why seek for newer guardians? Year by year the earth put on her robes of leaves and sweetest flowers — the rich harvests waved over the corn-fields, and the fruit-trees and the vineyards travailed as of old; winter and summer, spring and autumn, rain and sunshine, day and night, moving on in their never-ending harmony of change. The gods of their fathers had given their fathers these good things; had their power waxed slack? Was not their powerful hand stretched out still? Pan, almighty Pan! He had given, and he gave still.

Source: The Bhagavadgītā (1973), p. 75. (10.)

1860s, Fourth of July Address to Congress (1861)
Context: And this issue embraces more than the fate of these United States. It presents to the whole family of man the question whether a constitutional republic, or democracy — a government of the people by the same people — can or can not maintain its territorial integrity against its own domestic foes. It presents the question whether discontented individuals, too few in numbers to control administration according to organic law in any case, can always, upon the pretenses made in this case, or on any other pretenses, or arbitrarily without any pretense, break up their government, and thus practically put an end to free government upon the earth. It forces us to ask, Is there in all republics this inherent and fatal weakness? Must a government of necessity be too strong for the liberties of its own people, or too weak to maintain its own existence?

Ur-Fascism (1995)
Context: The followers must feel humiliated by the ostentatious wealth and force of their enemies. When I was a boy I was taught to think of Englishmen as the five-meal people. They ate more frequently than the poor but sober Italians. Jews are rich and help each other through a secret web of mutual assistance. However, the followers must be convinced that they can overwhelm the enemies. Thus, by a continuous shifting of rhetorical focus, the enemies are at the same time too strong and too weak.

Reflections on the Revolution in Europe (2009)