There is a certain kind of financial advice that assumes you are a robot. This robot wakes up at 5:30 a.m., tracks every expense in color-coded spreadsheets, never impulse-buys anything, and derives emotional satisfaction from optimizing its Roth IRA contribution timing. You are not this robot. You are a human who sometimes forgets to cancel subscriptions, buys coffee because mornings are hard, and occasionally spends $47 on something you don’t remember ordering until it arrives. And yet—despite not being a robot—you probably do invest. Or want to. Or feel like you should be investing more. That’s where leftover capital comes in. Not the dramatic, life-changing, sell-your-car-and-move-to-a-lower-cost-state kind of investing. But the quiet, unglamorous, psychologically sustainable kind that comes from money you didn’t even notice staying in your account. The money you didn’t spend on coffee this month. The money that didn’t get swallowed by takeout. The money that survived yo...