It is the function of the Game Master to give players as much rope as they ask for–above and beyond the 50′ each member of the party is obligated to carry–that they might hang themselves. Running a game is very much like writing a horror story–the more you leave up to their imaginations, the worse the situation gets.
Most of the players in my ongoing D&D 5E campaign are relative neophytes. For many of them, I’m the only GM they’ve ever known. They are pushing 5th and 6th level for the first time. With the exception of my longtime friend and resident optimizer, they have yet to fight their first dragon, cast their first Teleport, etc etc. But I think I’ve done a good job so far–when we had a couple of guest players, both veterans, they asked me after the session: “They’re so afraid–What did you do to them?”
To get to this delicious level of Player PTSD, I’ve relied on one of the classic DM tricks–tell them what they sense. It’s amazing what adding a couple of so-called weasel words can do. For example, tell the players that “There seems to be a large pile of gold in the center of the room” or “The bridge appears to be solid.” If you’ve done your job, they will approach it with fear and trepidation.
Eventually, this trains your players to ask smart questions, actively telling where they look and what they do. I really like how 5th edition goes back to the old Search mechanic–while you do have the Investigate skill to get you started, the players are really supposed to tell you how they’re searching the wall. “I roll to investigate” and “You find a hidden door” pales in comparison to “I check the bookshelf, nudging the books out of line to see if any of them are attached to a hidden lever.”
It can also have some unproductive results, however. Some of my players are complaining that they spend a great deal of time cautiously poking around empty rooms and normal hallways. It’s also led them on some wrong turns–over the last several months they’ve been exploring the same megadungeon, in search of a mystical Forge, and each time they try to locate it they pick up on a clue that may or may not be real and end up hilt-deep in another fight against damage resistant Helm Horrors.
Finding the balance between letting the players truly explore on their own vs guiding them towards the best content is tricky. It’s easier when you make sure that everything the PCs can do in your gaming environment is interesting, but that involves a great deal of prepwork (or some truly excellent improvisation).