Derail

A derail attempt is an attempt by an individual or group of individuals to take a topic or thread off it's original topic, usually as malicious means. It can also very rarely occur naturally as part of topic drift.

Purpose of usage
Derail attempts can be used by various types, especially if the topic is unfavourable to their views. However this is a classic intel tactic to cause a thread which may progress into a naturally constructive investigation and thus threat to be redirected off-course.

This is usually the intent of doubt-casting, to throw people off of a valid and/or reasonable debate into an unreasonable and thus invalid one.

Counteraction
Users should use re-rail approaches as well as ignore tactics on any doubt-cast or troll bait attempts.