I don't play Fate so I don't actually know what that reference is.
I'm thinking of something pretty straightforward: for whatever reason, you know that you are probably going to succeed at something, given the DC and your bonus. So you go for a little more, get a little more ambitious. Because you're trying something harder, you roll with disadvantage. If you still succeed, the results are all that much more impressive.
I mean, really, it's quite similar to the -5/+10 of GWM and Sharpshooter, but using disadvantage.