Splitting a bill sounds simple until the numbers don't line up: one friend covered the whole table, two others chipped in for drinks, and someone paid the tip. Rather than pass cash around the table, note who paid for what and let the totals reconcile. Everyone ends up even, and it takes seconds.
Because people rarely consume equally, and — more importantly — because different people paid different amounts up front. A flat divide ignores who already fronted money. Splitting by who-paid-and-who-owes is what actually leaves everyone square.