Memory Sequence 11:
For this trophy / achievement you must complete the entire 11th level without walking into an enemy's field of view. When an enemy sees you and their vision cone turns yellow (or even red) you must restart the checkpoint immediately! It is okay if you throw fire crackers and noise darts to distract enemies. Do not throw daggers at them though, as they will automatically detect you if you do.
Just follow the exact path I take in the video. If you mess up you can restart the checkpoint as often as you want.

After each section with enemies you will get a bonus award and see your statistics. It must always say "Times Seen: 0". If it's not at zero it means you have been detected and will likely have to restart the level from scratch if you've already passed the next checkpoint.