Go Down the Rabbit Hole

To follow a thread or a lead that branches off from your initial objective, then (often) doing that repeatedly to get your self lost and/or completely off topic. This is based on the fact that Rabbit Holes (or "warrens") are often interconnected dens and tunnels with no apparent pattern to them, but in which one would surely get lost if followed impulsively. (See also: lost in a maze, or trapped in a labyrinth.) (This predates Lewis Carrol, whose meandering fantasies are very much like a random stream-of-consciousness exercise.)