If I understand it, the point is to avoid cash transactions that cannot be taxed. One article I read pointed out that the 30% would include rent or mortgage payments, utility bills, and such things.

Personally, I would find it easy to hit almost 100% of the transactions I make electronically - I use cash rarely now (living in France, no cash tips etc.).

I think I would struggle to only spend 25% of my income, though. Even if I am saving a lot, once I pay rent, family groceries, utilities, phone and internet, I’d be past that. If you don’t mind to share, how do you manage to spend so little of your income? There’s always room for me to save more, and I’d love a couple of tips.