I don't know if this counts, but I'd say the Enlightenment. It was a discovery in that we discovered a new way to interpret the world.
I think there is kind of a glass ceiling when you talk about fire, plumbing, electricity and so on. Each one was a necessary stepping stone to get us where we are, but without any one of them, we wouldn't be here.
The Enlightenment gave us a brand new sense of autonomy as a species, which in turn has given us a greater amount of control over "Destiny."