sometimes the hijack is of equal interest to the poster and adds depth and a sense of support even if not quite the answer to the question. Maybe we can rename this as "side trip". Sometimes the hijack is done after the question has been addressed and allows for a little levity before coming back on topic. we can call this a "rest stop"?

Or maybe I am justifying my own tendency to hijack threads ...

I am usually happy for anyone to hijack my own threads - it provides a sense of support which is always part of the reason for posting in the first place - otherwise I would just Google everything wouldn't I?