[Warren Buffett knows that he] is not immune to the allure of irrational behavior. He is what Behavioral Economists call a sophisticate: someone who understands his irrationality and builds systems to cope with it. (The other types of people are the "rational," who never deviate from optimal behavior, and the "naifs" — unaware of their irrationality and therefore unable to address it.)

Uncommon a person as he was, Buffett had a very common concern: he feared gaining too much weight. Rational agents don't gain weight because they always consider all the possible consequences of all actions. Naifs plan to start their diet tomorrow.

But Buffett — who breakfasted on spoonfuls of Ovaltine — understood his predictable irrationality: people eat without consideration for the long–term effects; that's why they gain unwanted weight. Being a pragmatic person, he decided to curtail overeating with a commitment device.

He gave unsigned checks for $10,000 to his children, promising to sign them if he was over target weight by a certain date. Many people use commitment devices to try to keep their weight down, but Buffett's idea had a big flaw: his children, spotting a rare opportunity to get money from the notoriously frugal billionaire, resorted to sabotage. Doughnuts, pizza, and fried food mysteriously appeared whenever Buffett was home.

In the end the incentives worked: even with his children's sabotage, the Oracle kept his weight down, and his checks went unsigned. But had he been purely rational, no commitment device would have been needed.

— Dan Ariely, Warren Buffett and his attempts at self–control