User blog comment:Epic~00/In Defense of: Dave/@comment-24971793-20150320214725/@comment-24152851-20150322013607

It's only derailment when it's an unexplained, unreasonable personality change. Typically resulting from writers not doing research, or having bias towards particular characters. If it's justified why their personality changed drastically (mutation, epipen, blue harvest moon), then it's not really derailment.