Explain scarcity as the gap between limited resources and unlimited wants, and why it forces choice.
Economics begins with one uncomfortable fact: there isn't enough of everything for everyone to have all they want. Time, money, oil, teachers, hospital beds — all limited. Wants — comfort, entertainment, security, more of everything — effectively unlimited. That gap is scarcity, and it isn't a temporary glitch; it's the permanent condition every economy exists to manage.
Because of scarcity, every person, family, business, and nation must CHOOSE — and every choice is really three questions: what gets produced, how, and for whom. Different systems (markets, command economies, traditions) are just different machineries for answering those three questions. Watch for scarcity today: every line, every price, every "sold out" is scarcity showing its face.
Mastery looks like: They can define scarcity precisely, distinguish it from shortage, and spot it in daily life unprompted.
Common stumbles: Treating scarcity as poverty (it applies to everyone) or as shortage (it never ends).