My point was that the NPC not being able to go get an assassin *at the time*, because there were no assassin's in town and the nearest assassins were days away was not a big deal to me, because assassins could be brought in later if it made sense keeping within the "world building that had been done prior. To some people having world building and maintaining verisimilitude within that structure is a bad thing. To those like myself, it is something desired. The world building defines the setting on a large scale and answers certain questions ahead of time (what is the geography? What is the planar cosmology? Whom are the deities and how active are they (if there are deities)? What is the nature of magic in the world? What are the various nations and cultures available to PCs and what are they like (what are their beliefs and values? What is their government like. What is their technology? what classes/class variants/ subclasses are available)? What are some of the major institutions found in each culture? Whom are some of the major NPCs? What is some local history? Are their any major monsters in the area or other information that a starting player from a specific region or city might have that other starting characters would not?
Now, as for the specific instance with the wizards and assassins, I did not plan to have assassins hired. However, back when the guild was created, it crossed my mind that the head of the guild and the rest of the leadership would be the type to keep tabs on their members and they used the guild rings to track movements and, at times spy on them. When the rogue removed a guild membership ring off the finger of a wizard guild member's corpse and pocketed it, I remembered about the spells on it and the rogue never sold the ring or had it identified. The player kept it in the pouch and forgot about until a year or more later while going through his list of items.
See above. For a year or more, the players (and their characters) had been wondering how they had been tracked. Then one day, the rogue pulled it out and put it on. The druid thought he saw an eye, momentarily, appear in the gem and inquired about it. Upon the rogue telling how it came to be in his position, the druid cast identify on the ring(back in 3e, identify was one of the arcane spells that l had put on a variant druid spell list). The rogue got a stern lecture from the druid and then the party about giving rings and other items found to the druid- especially, if taken off dead wizards.
The players themselves loved how they had been tracked, how it made sense, and how the guild, probably, would have forgotten about them much earlier in the campaign if the rogue had not taken the ring).
Would I have thought of a guild ring if I had not created the guild prior to play and had to improvise the guilds creation on the spot? Probably not. Most of that initial adventure was improvised, but the groundwork was laid out with information I had determined back when coming up with the various nations, their cultures (government, beliefs, value, etc.), major institutions, major npcs, local histories,
etc.
Now, that all stated, while I like to engage in some world building to help define the world, it cultures, etc., I personally don't take it to the Tolkien level. I want to answer basic questions about the world, define how things work (e.g., cosmology, magic), and give players the available races, nations and cultural information that grounds the characters into the setting (including what classes, class variants, and or subclasses are restricted to specific cultures). This information is not all provided at once. Some is information is reserved until a player chooses a specific race, culture or even class.
The same information also helps me to improvise when my players go in completely different directions or pursue a different goal mid adventure. It also helps when they present opportunity for side adventures (e.g., complaining about being unsuccessful in getting the druid laid in the previous city...just as they are near a fairy forest led to the druid being kidnapped by a fairy and the party trying to rescue him before he either eats or drinks anything or becomes amorous with the fairy).
