If you're starting a business these days, starting with the premise that banks offer a dreadful experience isn't likely to be a tough sell.

Josh Reich, co-founder of the online bank Simple, doesn't hold back:

"Fundamentally, banks make money by keeping customers confused," he says.

Reich is speaking of the major fees banks charge for foul-ups such as overdrafts. Speaking from personal experience, overdrafts are easy money for banks, since they can easily afflict anyone who isn't rich and doesn't have a flawless grasp of their daily cash flow.

But curbing overdraft fees by not letting customers spend more than they have isn't really the consequential part of how Simple is trying to overhaul the standard consumer banking experience.

Simple operates on the, ahem, simple notion that showing you your total account balance all the time is not the best way to get you to spend less and save more.

Instead, Simple has made a simple (there's that word again) yet powerful design decision: rather than highlight your total balance, Simple tells you what's "safe to spend." Incidentally, the app also looks great doing what it does: unlike so many banking apps, good looks and usability are a Simple priority.

Simple tracks your monthly bills and savings goals. Through the magic of addition and subtraction, Simple arrives at a number that more accurately reflects how much money you actually have to spend, rather than a number that tells you how much money you have in a fantasy world where you don't have to pay rent.

This little hack takes its cue from behavioral economics and the easy-to-believe (again based on personal experience) idea that we won't always make the most rational decisions about our personal finances even when we know what the most rational decision is. If we accept our fiscally flawed characters, then the next-best option is to trick ourselves into doing the right thing.

When we met, Reich drew me a simple bank-balance graph of a person who gets a regular pay check every other week. After payday, there's a short plateau, a steep drop, then a slow downward trickle until the next payday comes around. A parallel graph charting spending has sharp peaks and troughs reflecting what so many of us do: spend more than we really can afford when we're flush, then pull way back as we get close to zero.

These peaks and troughs correspond to feelings of irrational optimism and the inevitable financial hangover, Reich says. The goal of Simple is to smooth out the jaggedness of typical spending habits. As the graph gets smoother, he says, with fewer highs or lows, people feel better.

"Over that period between paychecks, you have those emotional swings," Reich says. "If you can reduce that volatility, you feel control."