I've been running a lot of fate and cthulhu-dark games lately, and I've run into a common challenge with several players: They'll roll the dice before we establish what kind of action they're taking and how (and, for Fate, what the difficulty of the roll will be).
This leads to all kinds of problems, because these are things we should decide before knowing the outcome of the dice so that our choices (on both sides of the table) aren't influenced by the random element which should rise out of those choices. In the case of Cthulhu Dark, it often means they rolled the wrong number of dice!
This is a minor blip in the grand scheme of things, but it's disruptive to the momentum of the game nonetheless: we stop to negotiate whether/why to re-roll, or try to make decisions which should influence the outcome while the outcome is already known.
Should I just crack down on the behaviour and force re-rolls every time, or is there a kinder, more gentle strategy? (I'm not even sure cracking down will be effective; it took a year of enforcing "roll on a manual and if it falls off, re-roll" to get them to regularly be able to keep dice rolls on the table.)