Sure, you can disable Focus in Options. But I can't believe no one has mentioned that you can incorporate this achievement with...
...by disabling Focus in the Custom Difficulty setup.
It's in the first section, Classic Thief Mods. Having No Focus
turned on awards you 50 points toward the 700.
I much preferred using focus throughout my first run (on Thief difficulty), then doing without it during the Master/700 playthrough. And having it disabled certainly took the worry away from accidentally hitting
, especially after having used it enough in my first run that it became a habit.
A comment in the other solution mentions needing Focus at the end of Chapter 3 to find the symbols. Although Focus makes it easier to find them in those little alcoves, no, Focus is not required there, nor anywhere else for that matter.
This achievement will pop as soon as you
pass a loading screen, and begin Chapter 8.