Fate Core has a concept of “success with a cost”. It’s a rather difficult subject for people coming from other systems to wrap their head around. Basically, even if a player fails to meet the difficulty, they can still succeed – provided they are willing to accept the cost of that success.
Here’s my slightly expanded take on what it means to succeed or fail. Success means that the player gets what they want on their terms. Anything else is a failure, even if what they were attempting actually gets done. Success at a serious cost and completely failing to accomplish the task are both the same thing if it’s the overall goal that is failed as a result.
Getting into this mode of thinking can take some doing. The first thing that has to happen is the players and GM need to be completely upfront about what their goals are, and what is at stake. While the GM should have say over what success at a cost actually means, in order to make an informed decision on whether to accept it the player should know what success, a tie, outright failure, or success with a major cost will result in beforehand. Also, the goals should be set appropriately.
An example would be a character who is being forced to hack into a system in under 60 seconds or the Big Bad Guy will blow his boyfriend’s brains out. The main question should be: is hacking the system the goal, or keeping the boyfriend alive? If it’s the former, than failure or success at a cost on the roll would be logically related to the hacking itself (I’m not saying it has to be, just that it follows). If the goal is to keep the boyfriend alive – which is what I think it is – then this drives the narrative of exactly what happens on a failure. Either the boyfriend is getting killed, or there is going to be some other cost. For success at a cost, maybe right at the 60 second mark, the character yells out, “I found a back door! Give me a few seconds!” and the Big Bad Guy shoots the hacker instead, giving him a minor consequence, to show that he “meant business.”
There are a lot of ways to go about this, and most are going to be completely dependent on the context. But keeping an eye on the appropriate goal can help make the distinction between a success and a failure, even in cases where the player chooses success at a cost.