Why Does the GM Say "No?"

I keep trying to do stuff in the game, and my GM keeps shutting me down. Why does my GM keep saying "No?"

Contrary to how it seems sometimes, GMs don't, as a rule, say NO arbitrarily. There can be several reasons why your GM says no to something you want to try, and we may not always be as clear as you need in explaining it. Here are some of the reasons I've said NO to players in the past that may help clarify for you why your GM has said NO to you on occasion.

• General vs. Specific Attempt - A player states, "I'm going to pick that lock." He rolls the die and fails. Then he says, "Okay, I'm going to use my dagger to try to pick it." The GM says NO. Why? Because you already tried a general attempt to pick the lock and failed. Deciding to use a specific tool to pick the lock is not a substantial change in circumstances to justify re-rolling the dice. You failed a general attempt to pick the lock, and in that general attempt it is imagined you exhausted all tools at your disposal in doing so, including borrowing your companion's lock-pick set. To find reasons to keep rolling the attempt until you succeed it is disingenuous and a clear attempt to game the system.
• Can I Have Advantage? - Players ask for advantage in a task roll for all kinds of things, and the GM must decide in a split second whether an advantage can be allowed under the circumstances or not. "I've climbed a tree, can I have higher ground advantage in combat? NO, sitting in a tree is a precarious position, any advantage you may get from higher ground is negated by the need to keep yourself from falling out of the tree while you swing your ax at the enemy. "I have night vision, can I have advantage to surprise on any guards we encounter?" NO, because the dwarf guards have dark-vision, which is similar to night-vision. "I have enhanced hearing, if I put my ear to the floor, can I have advantage in determining the direction the monster is coming from, in spite of the confusing echoes you described?" NO, that would take a sensitivity to vibration, not hearing.
• Too Complex an Action - Sometimes a player wants to do too much in a single action: "As I climb the ladder, I'm going to hold the little princess's hand and keep my sword out in case there are guards waiting for us at the top of the wall." You only have two hands, if you hold on to the princess with one and your sword with the other, how are you going to hold onto the ladder?
• Acting on Knowledge Not Evident - It is unavoidable sometimes that the players will overhear things during the game that their character couldn't possibly have learned themselves. For example, while Jerold's dwarf is guarding prisoners at one location, clear across the compound an NPC reveals to Mick's character that the guards have placed a spy among the prisoners. Now Jerold suddenly wants he dwarf to search the prisoners to determine which is the spy. Of course NO!
• Acting Against Character - A cleric who, in all previous adventures, has shown nothing but deference for nature and compassion for all the gods' creatures, suddenly wants to order his pet ferret to deliberately get caught up in the giant spider's web to lure it out so the party can attack it. In D&D they call it Alignment, in other games it may be nothing more than the characters past action that define her, but in any case, your GM is often going to tell you NO in such cases.

As I've noted before, it's easy to get frustrated and look at your GM as your enemy, but he/she isn't. On the other hand, keeping a fun, challenging, and consistent world flowing beneath your feet, as players, can be a challenge. If we say NO it's almost always for a very good reason.