1. Why is this thing different than what we currently have (centralized fiat)? 2. Why is this thing useful in the real world? 3. Why is this thing real, reliable/consistent, and secure? I feel these three are the bare minimum concepts one must grasp to have a high school level understanding of Bitcoin and why it matters. I suppose I could add understanding inflation as number one, which would basically serve as an understanding for why limits on supply would even matter.