According to Isaac Asimov, the truly important scientific discovery was when Benjamin Franklin published his paper in 1752 stating that "lightning is an electrical phenomenon."
As they say, it's no exaggeration to say that this changed everything. Previous scientific discoveries were only important to other scientists; they had no bearing on humanity as a whole. When Galileo published his geocentric theory, the church opposed it, but it didn't make much of an impression on the general public.
However, Franklin's discovery led to very practical applications.
This is one of Franklin's "lightning rods," a device designed to prevent lightning from striking buildings.
This spread like wildfire, like, "Oh, I don't know, maybe it was lightning?" Within 10 years, churches were the only ones not using lightning rods, because they believed lightning was the work of God and a specific reward from Him. However, after lightning struck a church where gunpowder was stored, (perhaps because God likes churches?) churches also began to adopt them.
The idea that science can solve real-world problems began with lightning rods, and before we knew it, the strange phenomenon of "electricity" came to be used for all sorts of purposes.
For motors that do not require flames,
Bright, inexpensive, and safe lighting,
For extremely fast computers, etc.