If you ask me? Mobile/WiFi internet… The way and amount of time we use our phones had changed A LOT since their diffusion. I guess the release of the iPhone changed our idea of what a phone is too
Edit: when I say modern world I’m referring to the last 50 years. So stuff like “the electricity” or “the telephone” doesn’t count.
The most?
Fire.
The best guesses right now is that our ability to use fire–and eventually create fire–allowed us to evolve the brains that we have now, because cooking food significantly decreases the energy needed to process it, which allows more energy to be used by your brain. And our brain burns a lot of calories. Cooking food is essentially a preliminary digestion process. Without our brain, the modern world as we know it never exists. Hell, we never even evolve past troops of apes.