Topic shifting

Overview
Topic shifting is a rhetorical deception where one person in a discussion (the shifter) manages to subtly change the discussion's topic to another, related but different topic, without explicitly announcing the change of subject or reaching any kind of mutual agreement that such a change is appropriate.

Reasons this is done include:
 * The shifter feels better able to defend their point of view on the second topic than on the first (which is not a legitimate reason for changing the topic, but the shifter may be doing so without realizing it)
 * The shifter views "winning the argument", or even "not losing the argument" (e.g. allowing or encouraging the argument to devolve in chaos, if a victory seems unlikely) as more important than working towards a better understanding of the truth on the original topic
 * The shifter truly sees the second topic as being at the heart of the disagreement about the first topic (an honest and conscientious arguer will state this point specifically so that the change can be discussed, in which case it isn't "shifting" but a legitimate change to the focus of the discussion)