It's the same old story. A person holding the money of others in trust. A difficult moment arrives. The guy with the money decides to borrow a bit of it, just enough to weather the storm, just for a short time. He takes some of the money. He breaks the taboo just that once. He takes the money telling himself that he'll put it back before anyone even knows it's gone.
And from there on in the theft takes on a life of its own and grows bigger and bigger with each passing day. In very short order the void created from the theft becomes too big to fill, too big to cover up and then the original theft simply begets a continuum of ever larger thefts necessary to disguise the truth.
For Bernie Madoff this wasn't about the money he misappropriated. It was about what would happen to him, to his exalted reputation, if and when it was discovered. He didn't break the taboo because he wanted a few bucks, he broke it to protect Bernie Madoff and everything he'd built.
It's hard to say how often these scams work. They're very difficult to conceal in the long run and that's probably what sets Madoff apart from his garden variety confreres, the lawyers who bilk their clients of a few million. He got away with it for at least two decades while regulators somehow looked the other way, even ignoring specific warnings.
Madoff probably realized shortly after this began that there was no good way out for him, that the only thing undecided is when his day of reckoning would arrive. Unfortunately for his victims, Bernie Madoff didn't have the decency to turn himself in years ago.