'Story Teller's Discretion'.
This phrase indicates the Story Teller (or
DM, or
GM, depending on what game one is playing) decides to make reality shift in a particular
way. Often-times done in order to make the story develop in a particular manner.
1. Upon reaching the anti-climactic 'Final Encounter' of a
long and drawn out quest for the artifact needed to enter the Bastion of
Broken souls (A fragment of the soul totem), Fighter: The human fighter rolled three natural twenties in a row, which resulted in the untimely (one-round-kill) demise of the fallen god.
However, in order to promote the challenge of this encounter, the DM decides to use an STD to allow a centuries old Contingency heal to revive the poor fellow, at full hitpoints, and rather angry at having been slain in such a way. Then a '
true' fight ensued.
2. Thor throwing his famed
hammer Mjollnir(Molniya) at a Werewolf in D&D Edition 3.5, and deciding not to remove the 10 damage which would be removed, since the
hammer isn't made of silver. This STD though perhaps un-needed (the werewolf would likely die from the modified damage) makes sense, since even though it's not a silver
weapon perse; when Thor throws his
hammer, he means business, and that 10 damage shouldn't be reduced because it's not made of silver.