As used in QFS, a thought loop is a circular argument that a person presents either to self or others usually for justifying some belief or habit.
Thought loops can also be used in debate or debunkery. The neurolinguistic idea is that the thought loop is longer than fits in short term memory, so that contradictions and non-sequiturs become harder to spot. Individually taken, the thought loop's steps may seem quite reasonable. Still, the thought loop is an after the fact rationalization. The formation of the thought loop does not have to be a conscious attempt at deceiving self or others. These can form simply from habit. An important characteristic of a thought loop is that the argument always follows a fixed sequence of associations and is very difficult to break by interrupting the person running the thought loop. It is as if the person were hypnotized to follow only one track of thinking. This same effect makes thought loops hard to spot in self.