Quote from Sir Walter Scott's poem, Marmion, usually wrongly attributed to Shakespeare:

"Oh what a tangled web we weave when first we practise to deceive"

An explanation from enotes:

"...and so the cycle continues. The "tangled web" metaphor refers to the act of a spider spinning its geometrical home: if it becomes tangled, the points do not intersect as they should, and the web becomes a mangled mess, much like the act of keeping up with one's own dishonesties."