The story
Attributed to canto 6, stanza 17 in the poem Marmion (1808) by Sir Walter Scott: "O what a tangled web we weave/ When first we practice to deceive"
Etymology from Wiktionary, CC BY-SA 4.0.
what a tangled web we weave when first we practice to deceive
Today it means: When one tells a simple lie, it may become necessary to tell more complex lies, eventually spiraling out of control and leading to the exposure of the deceit. Full definition →