Interesting, so, then, you're saying that if the players never need any specific item for anything, because they can just use something else or accomplish their goals in a different manner. This would imply that prep is pointless, because the players can just decide they want to do a thing a different way, and whatever way they choose must be allowed to work?
You don't prep based on the player's goals, you prep based off the NPC's goals and whatever events occur at whatever times. "The lich wants to obtain the forbidden book" is an adventure setup, but the players have the liberty to choose to grab the book before the lich or just attempt to kill the lich directly. Its not a McGuffin because its not mandatory for the players.
Edit: or they can just ignore the lich and deal with the new undead kingdom later, preferably when they're stronger.
I don’t know why prior determination by the DM would matter. This isn’t a railroad unless the PC have no choice but to investigate the map at all. If they can choose to do other things entirely and never follow up on the map, there’s no railroad.
The assumption I was under was that they were given false information by otherwise completely reliable sources in order for the DM to place them exactly where they wanted them to be.
Its like the players going to an inn when suddenly, the innkeeper is suddenly an evil Rakshasa and attacks them in the night, yet when players casted Detect Magic, Dispel Magic, True Seeing, and Identify on the innkeeper, none of them revealed the innkeeper to be anything other than human.
I just addressed this -- imagine that the players have chosen this item. Rerun the question. You're evading on spurious grounds.
If they
chose to pursue the item, they'd go in its proper location anyways because they made the choice to go there to retrieve the item. I can't decipher the meaning of your question.
This is placing information in specific places and denying player actions to recover that information solely based on where they look for it. This would appear to be railroading, because you've placed information the players want in a place other than where they looked for it, and denied action declarations because of this choice you made.
In reality, I'd have multiple pieces of worldbuilding information sprinkled everywhere, but none of its mandatory since the players come up with their own goals. If they decided they didn't want to investigate the people up north, the world doesn't end, the shady people just continue to do their shady business. World-changing events may happen but I rarely threaten the player's lives if they don't pursue a hook.
I don't care where they go, who they talk to, and why they're there from a narrative PoV, I'm letting them explore my world and make their own decisions.
For the record, slight railroading for players new to the game or easily overwhelmed by choices aren't horrible. They need somewhere to start. Even then, though, I ask them what they would like their first objective to be and I edit the world to ensure that objective exists. Want to pull off a heist? Great. Want to rescue a damsel? Perfect. Want to kill a god? Go for it. I'll let them choose the hook they want so their objective is easily pursued without a breadth of overwhelming choice.