You're on a track. It may be the DM saying to the player that their character can't decide to do something. It may be circumstances set up in the game that take away player agency. Whatever the mechanism, the PCs lack choice.
As a DM, I prepare settings and give the PCs a number of ways to approach the situation, but expect that they'll do the unexpected. As such, my mentality is that I'm creating the environment for them to play within, and they're directing he direction the environment needs to grow. In a railroad game, the DM defines the environment the players will play in and then directs how it will evolve as well by limiting their options.