In the course of a discussion of D&D tactics, it was brought up how in old school D&D the closest equivalent they have to "flanking" like in 3.5e is a thieve's backstabbing. While I'm not sure the analogy is necessarily the best, it got me thinking about what the most effective use of backstabbing is. For a thief to backstab, they have to use both their "Move Silently" and "Hide in Shadows" ability to move behind their target. Because the probabilities multiply, a quick calculation reveals that this is a high-risk endeavor for any thief. Following the Labyrinth Lord rules, a first level thief has a less than 3% probability of successfully backstabbing, and no thief stands greater than 50-50 odds until he is 10th level. Given that, my intuition is that the payoff for backstabbing is on average fairly low. I'd only recommend thieves choose to backstab in the face of a real risk of total party kill (TPK). To say more would require more modeling, though. Since I'm already behind on my Markov model for my elf versus an orc, it's probably best that I hold off on going much further on this one.