I'm looking for a famous idiom or saying that conveys the meaning:
Life helps us sometimes by giving us something that we can build upon, but we develop it into something bad, harmful or destructive.
The original saying in my first language, Arabic, portrays this image:
Every time the days give us "the body of a spear", we mount a "head" on it.
The body of a spear, or a rod, can be useful as it could be used, for example, to put up a tent. But once it has a head added to it, it becomes a weapon.