<p>There is a specific kind of frustration that comes from understanding exactly how something works and watching everyone around you overpay for it anyway.</p>
<p>Nik Storonsky understood currency exchange. He'd spent years at Lehman Brothers and Credit Suisse trading equity derivatives, watching billions move between currencies at razor-thin institutional spreads. And then he'd pull out his personal debit card on a weekend in Europe, and the bank would quietly take three percent.</p>