The Tesseract can't fight, but you can't protect against yourself.
6 seconds sound clip from the The Avengers (2012) movie soundboard.
You can hear this line at 02:00:47 in the Blu-ray version of the movie.
Quote context
[...]
- Doctor.
- The Tesseract can't fight, but you can't protect against yourself.
- It's not your fault. You didn't know what you were doing.
- I built in a safety to cut their power source.
[...]