Vicious cycle

Etymology

From "vicious" (Latin "vitium," fault, vice) and "cycle." The phrase grew out of the older logician’s "vicious circle," a flawed argument that assumes what it sets out to prove; it broadened to any spiral in which effect feeds back to worsen cause.

noun phrase · /VISH-uhs SY-kuhl/
A self-reinforcing sequence in which each bad outcome worsens the conditions that produced it, driving the situation further downward.
What it names
A feedback loop with a direction — downward — capturing how problems can compound themselves rather than settle.
Example
Debt forced longer hours, exhaustion hurt his work, his income fell, and the debt grew — a vicious cycle.
Related idea
The dark twin of the virtuous cycle, in which each good result improves conditions for the next. Both are instances of a feedback loop, the neutral parent concept; what makes a cycle vicious or virtuous is simply the direction in which the self-reinforcement runs.