In Tom Clancy's Splinter Cell: Conviction, one of the most difficult challenges that can be devised is to get to the end of a Deniable Ops map (by subduing all of the enemies) with these restrictions:
- pistol only,
- no gadgets,
- hand-to-hand kills only,
- one attempt (no retries, restart from lobby),
- Infiltration, and
- Realistic difficulty.
I haven't tried it on every map, so I'm wondering: Is there any map where it's physically impossible to complete it with these restrictions? I can't imagine.