So you've defined the world to begin with in such a way that the only way of success is the one way you want the problem solved? By RAW, for Pathfinder and D20, tracking a human down a cobblestone road is a DC 20 check, which a 10th level Ranger can plausibly not fail on a 1. No, it's not a dropped neckerchief; it's the horse excrement stuck to his shoe that's distinct because the horse fed on apples. To nerf a can't-fail ability to a can't-succeed ability is rather extreme.
Which is a perfectly reasonable adjudication. My problem as DM is that I might not think of the horse excrement idea during the game. I did not think of it earlier when posting my earlier post. So yes, with a quick thinking DM, that's a totally fine idea.
If the PC has abilities which are explicitly defined like "a 10th level Ranger can track down a cobblestone road with a DC 20 check", then no, I will not change the rules. I'm a firm believer of using RAW (unless it is a fairly bad rule). I was actually talking about if the rules do not actually exist and the DM is winging it.
It's a DC 20 check, so he made it by 7. By denying the check, you have effectively changed the rules of the game, and made Tracking and Survival much less valuable. This is not even a "Mr. Awesome can't be tracked"; this is a full-on nerf of the tracking rules.
It depends on level of plausibility. A different way of saying it is that as DM, I think that the DC is 30, so a 27 does not cut it.
The point is not to change the rules, the point is to not be bound by the rules if a given rule does not make sense to the DM, or to make a new rule that does not exist only if it is plausible.
In some cases, it does not make sense that a PC could track an NPC through a town with cobblestone roads. In real life, you could not do this shy of extremely special circumstances (like a blood trail). There's probably nobody on this planet who could actually track someone through a town with cobblestone or concrete, or other hard surfaced roads. Granted, PCs can do extraordinary things that people cannot do in real life, but I like things to be somewhat plausible.
So if there is an actual rule, I'll use it (5E does not appear to have a lot of DCs yet defined). If not, I'll adjudicate based on what is plausible.
No, the concept of "just say yes" goes hand in hand with "listen to your players' speculations and steal the coolest ones for what's really going on". It's about agency, it's about making what players do matter in a game instead of what works is exactly what the programmers thought of before hand.
Yeah, I think that we are just talking at cross purposes here. Player ideas are often used in my game.
What I am talking about is that a player's idea is not required to even get a dice roll in my game. Just because someone thinks of something does not mean that as DM, I am obliged to have the world change to incorporate that idea,
Simple example. A player wants to create gunpowder. Sorry. I don't want gunpowder in my game world. He will not be successful, no matter how well he rolls on an Alchemy check. Some DMs do not like the idea of saying "no" to the player, so they let them roll and hope for a crappy roll. I don't do that. I'll just tell the player straight out that gunpowder cannot exist in my world because a) I don't want it there, and b) it's metagaming thinking to even come up with the idea. The people who first came up with gunpowder did not first think of shooting projectiles at enemies, they accidentally discovered a chemical reaction that was then used for entertainment and only later on used for combat.
A player is not entitled to bring gunpowder into my world. Just like any other player idea has to go through the filter of my expectations of what is reasonable for my world. This does not mean that only my solutions to problems exist, it means that a different solution has to be plausible given the current framework of the campaign.
You want to track someone across a lake? Good luck. Most NPCs are not going to dropping things into the lake so that you can track them.
You want to search around the border of a lake to pick up tracks, sure. I might say give me 3 dice rolls and it takes 8 hours of time. Why 3 rolls? Because there are 3 different places along the lake where people recently were hanging out, only one of them is the guy that the PCs are trying to track. Each location has different DCs and different info given. I do not necessarily make it a single dice roll, just for the result that the players are looking for. I might, I might not. Note: in this case, I would not tell them to give me 3 dice rolls right away. I would order the searches and have them roll the first site, roleplay that info and decision making, and if they decide to continue searching around the lake, go to the next site, etc.
This does not mean that I will definitely try to mislead the PCs. Sometimes, there is only one check. It means that the campaign world is evolving as it evolves (sometimes on the fly in the back of my mind) and just because a player asks for a roll does not mean that he will necessarily get the information he is seeking.
"Just say yes every time" is not, in my mind, the way to play. Mix things up. Throw out some red herrings once in a while. Listen to your players ideas, use some of them. But do not necessarily use an idea, no matter how cool it sounds. Use the ones that work best for your world.