You know what I am going to say. I love the push mechanism in the Year Zero Engine.
Surely everyone knows by now. In (most) YZE games you roll a handful of d6, with the hope that one or more will come up 6. You only need one to succeed, but given that the “handful” might only be, say eight dice, the chances of a 6 coming up are not great. For that reason, the “push” is a way of rolling again, at a cost.
The cost is different for each game. And the brilliance of that is the push mechanism, and the cost, helps the game evoke the world it is creating. The most elegant example of this is stress in Alien RPG, but I love the the Banes in Forbidden Lands just as much. They keep combat short and bloody and make that world feel like, well, like it’s been written by Joe Abercrombie.
A lot of people don’t like the non-linear probability of throwing a handful of dice, twice, and still not getting a single six. But my advice to GMs faced with players demanding that a 5 should also count as a success is stay firm, only ask people to roll dice when it matters, when something interesting will happen if they fail. And encourage players to pay the cost of pushing. It’s a brilliant narrative generator.