This is exactly the kind of small, everyday decision where "just grab one" quietly costs you money. Mio doesn't care about the walk to the machine — here's the math.
The same 500ml bottle of tea or water is priced completely differently by where you buy it. A vending machine (jidōhanbaiki) is the most expensive convenience: ¥150–180. The supermarket or drug store sells the identical bottle for ¥80–110 (often cheaper in a 6-pack). Brewing your own tea at home and carrying it in a tumbler (mycha, "my tea") costs roughly ¥20–40 per fill in tea leaves and water. Illustrative — prices vary by brand and area.
| Where you buy | Per drink | × 365 days |
|---|---|---|
| Vending machine | ¥160 | ≈ ¥58,000/yr |
| Supermarket / drug store | ¥95 | ≈ ¥35,000/yr |
| My tumbler (home-brewed) | ¥30 | ≈ ¥11,000/yr (a few thousand for tea only) |
Switching from vending machine to supermarket saves roughly ¥23,000 a year for the same drink. Switching all the way to a tumbler saves closer to ¥45,000 a year — the price of a used bicycle or a domestic flight, spent ¥150 at a time.
¥150 doesn't register as a decision. It's below the threshold where your brain flags "should I?" — so it's never counted, never compared, never questioned. That's precisely why it adds up. A cost you don't notice is a cost you never optimize. The vending machine isn't expensive per press; it's expensive per year, and the year is invisible.
The honest nuance: convenience is real. On a 35°C August day, walking past the machine to hydrate is worth ¥150 — heatstroke costs more than money. If you're out and thirsty with no shop nearby, buy the drink. The point isn't "never use a vending machine." It's: know it's the ¥58,000/yr option, and make it the exception, not the default.
Default to a tumbler you brew at home; buy from the supermarket in packs; treat the vending machine as the emergency option. The "right" answer isn't about willpower — it's about which drink is quietly running your meter every single day.