There's certainly a point of diminishing returns, and I'd even agree that it is a cliff. Once you have a decent place to live, and your day-to-day worries about paying the bills are covered, and unexpected emergencies do not threaten your ability to get to work, keep your job, and pay your rent, then for most people more money has a diminishing impact on happiness. But that amount of money is quite a bit more than the poverty line.