Three-card-monte can take all your money in fewer than eight minutes. Long cons can take days, weeks, months or years -- just ask Bernie Madoff.
The con artists generally have to put up significant amounts of money to pull it off. They usually enlist others and must gain use of offices and facilities.
On top of that, they have to think on their feet because many things can happen over time.
You've got to be good to run a long con and in one case we'll tell you about, the sucker took the bait, then came back so the same con could be run on him again.
For the scammers, that's a great ROI!