I won't say much more here but this second question caught my eye, because the answer is the same as for your earlier question. Some impactful work I am intensely proud of also became a thing that haunts me (or at least challenged my idea of "doing good").

Think about dual-use. You may never really know quite how your creations pan out. Not quite in the league of Mikhail Kalashnikov, but it piqued my now intense interest in tech ethics.

EDIT: damnit seems like everybody here is in the same boat. So mine was a gesture detection for medical robotics control that was repurposed for look-and-lock air combat (fire and forget a2a missile. An important caveat is I'm not even a "pacifist" and went in eye's wide open with a defence firm. I just wish they'd told me more up front that this was "generic tech" I was developing.