Groucho Marx once described W. C. Fields as, “a great friend and a great drinker.” Once, visiting Fields’ house, he was shown an attic full of alcohol. “Bill,” Marx said, “Prohibition has been repealed.”

“Yes,” drawled Fields in response, “but it might come back!”

In addition to his fondness for ethanol, Fields was also the guy who famously explained that you can’t cheat an honest man. (Fields never commented on whether you can cheat an honest woman. Ever the misogynist, he’d have discounted the possibility of ever encountering one.) You can’t cheat an honest man because the whole structure of a successful con depends on the weaknesses of the “mark” — the target. We’re continuing our taxonomy of management decision-makers this week … last week we talked about lawyers … and sadly, there are many managers who are easy marks.

What makes a mark the easy target of a con is his (or, with all due deference to Fields, her) desire for something. It might be the result of greed, laziness or another of the seven sins. Whichever it is, the mark will readily accept even the flimsiest story that reinforces his desire. Employees sneer at manager-marks, and manipulate them without much trouble. It’s easily done: Just tell the mark how your program will satisfy his craving.

Then there are zealots. Guided by pure principles, unmitigated by inconvenient practicalities, zealots need few facts to reach a decision. Their principle might be Microsoft-is-bad, Microsoft-is-good, closed-source-is-evil, open-source-is-communism, or any other high-concept belief. Whatever it is, it defines the zealot’s universe. Principles are postulates, not conclusions, so evidence is irrelevant: When a principle fails, it’s because the heathen prevented success. Zealots rarely succeed in management. The politicians (one category of heathen and the next category of manager) don’t let them.

Where zealots are guided by pure principle, politicians are guided by one principle: Organizational palatability. Politicians start by judging whether a decision will be acceptable and work backward to an explanation of why it’s a good idea. They’re the cockroaches of organizational ecology — highly adaptable, but not particularly desirable. Strong on survival and weak on accomplishment, they’re remarkably hard to eradicate. Leaders who like to talk have a hard time recognizing politicians. Those who spend more time listening identify them without difficulty, as they have nothing interesting to say.

There’s nothing wrong with the self-interest of the mark, the principles of the zealot, nor the adaptability of the politician. It’s their one-dimensional decision-making that causes all the trouble. Next week we’ll wrap up this series with other types of decision-makers who take a more balanced approach.