How can 21,000,000 BTC be enough for Earth?

The problem wasn't the pizza. Nothing changes between the two examples.

The 'problem' here is that prices are set in one currency, and the currency you are using is volatile against that currency.

Say the lambo store prices in BTC. You want to spend USD. Bitcoin is gaining today. When you walk in, the price is 5BTC, or $500,000 USD. When you're done selecting options, the price is still 5BTC, because it's priced in BTC, but Bitcoin is up 10%, and now the USD price is $550,000.

"But what's priced in Bitcoin?" You ask? Not much yet, admittedly. But that's the whole adoption thing. And yet, the exact same applies when dealing with two separate fiat currencies.

Say, instead of Bitcoin, you're a Brit, and your bank account is denominated in GBP. The dollar is rallying against GBP while you're buying your Lambo. You have the exact same 'problem'.

This has absolutely nothing to do with Bitcoin itself. And yet, again, given Bitcoin's volatility is overwhelmingly positive, on average, over time, any such differences will be a net gain for you overall, unless that changes.

/r/Bitcoin Thread Parent