What I have observed is that without this level of meta-communication, once the campaign has begun the players believe that the character perspectives are what should drive the action, and are often unwilling to commit to anything offline until the proposition is put to them 'in character' and usually - unless someone is really willing to try and bend others to their will - this inevitably results in half baked participation or limited agreement to any given point. Simply put: why should the characters risk anything (their lives, reputations or relationships) without a very good reason?
The problem is that the reasons that the GM thinks are good (it’s supposed to be a game about mystery/adventuring), are not sufficient to satisfy the players. Many games have an overriding assumption that the PC’s will want to participate in a dangerous activity, such as exploring a haunted house, or delving into a dungeon, but if the players have invested effort in their characters to make them seem more ‘real’ and have genuine aims and relationships with the world – such an action, not well justified to the character, may shatter a players perception of game reality. Meanwhile, on the other side of the table the GM is confused because the players seem to be refusing to engage in the core activity of the game (exploring mysteries/dungeons etc.).
My solution? Character buy-in is developed through in-game stakes. Characters need to begin with, or to have developed stakes in the game world, which they use to drive ambitions and aims, which in turn, levers participation in scenarios. Character developed stakes are critical to establishing the character, and taking the pressure off the GM to be responsible for everything. The GM has to allow the players to develop in-game stakes, and allow these stakes to be a partial focus of the game – then use these stakes, without destroying or co-opting them, to become the motivation for participation in the central plot the GM wants to explore. In other words, the GM is essentially ‘sharing’ the central plot of the game with the characters, which serves the dual purpose of allowing greater PC buy-in, and sharing responsibility for a fun game amongst the group.
Or, the GM needs to be up-front that the campaign requires the kind of characters that the players might see as ‘unrealistic’ or one dimensional and seek to develop some shared fun from this premise. If the game is about action and risk-taking, bring in the movie tropes, and use cinematic techniques to bring this to life for the players.
I’ve adopted the first approach with Kingsport Tales, allowing for detailed characters with developed back-stories that fuel their involvement in the Mythos, and used the second approach for Masks of Nyarlathotep Pulp Edition, highlighting that the game is a James Bond style action extravaganza. So far both games are delivering different, but equally good, levels of fun.