Good behaviour isn't relevant. And in a voluntary social pastime, I think ensure and expect are co-extensive.Yes, the DM has to be restricted if you want to ensure 'good behavior' instead of just expect it.
What I want to ensure is the following: dramatic needs => rising action => crisis/climax, with the content and outcomes being surprising to all participants, and in the role structure of mainstream RPGing which means that no one has to form a view as to what the story should be. Each can just do their distinct job.
What is at stake may be implicit, or explicit. If it's not clear, it's always possible to ask!But these declarations and putting your wager on the table as a player also means the rules are much more formal and prescriptive on the player side. At least that would be my expectation based on some comment of yours, not sure I would find that again thoughIt sounded like the player basically says something along the line of 'I want to achieve X and am willing to risk Y for it' and then that gets resolved. There is not really a formal 'and risk Y' in D&D
But I think it's correct to say that a lot of D&D play seems to involve dice being rolled in circumstances of low-or-no stakes, basically just for colour or a bit of "sound and movement".