A situation-specific explanation of why the player's command was unsuccessful. Such messages often drop hints, develop the backstory, or sustain a tone. For instance, when the player tries to take inventory in Galatea (Emily Short; 2000; Z-code), the refusal message is "What you're carrying isn't important," thus discouraging the player from trying to collect and manipulate objects. When a PC in Fine Tuned (Dennis Jerz; 2001; Z-code) tries to attack an NPC, the refusal message helps to establish character: "You hit Aloysius affectionately on the shoulder. 'Aw, cut it out,' he says, embarassed."
A generic, plain-vanilla message printed when the player tries to misuse an object is part of the object's default behavior and thus not really a refusal message. For example, if the player tries to ENTER a grate that is closed, the computer would give a standard reply: "But the steel grate is in the way."
A designer might personalize all of these plain-vanilla messages, in order to sustain a particular mood or tone: "The thick titanium alloy composition of your hulking robot skull protects you from damage as you lumber headlong into the closed grate."