An intriguing phrase: Baisser les bras, means: To throw in the towel, to give up, admitting defeat in a struggle, endeavour or fight.
Hehe.
So this came from literally lowering your arms when you surrendered - I imagine that lowering your physical arms included the arms (weapons) you held where surrendering means no longer using weapons in an attacking nor defensive stance. Not that I found this context when I looked up the origin of the phrase. But makes sense to me.