Irish people love Stripe, the payments processor founded by the Collison brothers. And Stripe is a great business and all – but it’s small fry next to Visa. Where Stripe handles more than $300 billion transactions per year, Visa does more than $9 trillion.  And Visa is interesting because, from an investment perspective, it’s a close to perfect business.   In the last few weeks, I’ve been writing about how the famous teacher Michael Mauboussin values companies. A lot of it boils down to something called sustained economic profit.  Formally, sustained economic profit is: ((profit divided by invested capital, ie debt…