DiscerningDM

The DM is the whole world and everything in it

With the exception of some mighty fine miniatures and Dwarven Forge terrain, players only see what the DM tells them. If the DM misses something, it doesn't exist. Good players will ask for details, or even roll skill checks to coax more description from a reticent DM, but oftentimes the burden falls squarely on a DM's shoulders to get all of the detail out on the table.