**This achievement is MISSABLE**
Playing any heist on any difficulty in loud, escape without ever aiming down sight.
NOTE:
Aiming down sight is done on mouse my holding down right click. If you keep accidently clicking the right mouse button, try removing "aim down sight" from your key binds. That way, even if you right click, the achievement is not lost.
You are still allowed to use laser-sights, as long as you do not aim down sight. The lasers can be turned on by default with the 'Q' button.
Pistols and Shotguns are easiest for this achievement.