During the Vietnam War, hundreds of thousands marched on Washington. A few years ago, Louis Farrakhan organized the Million Man March.

I fantasize about holding National Boycott Stupidity Day and getting the same kind of turnout — throngs of citizens tired of popular culture’s ongoing celebration of idiocy and ignorance as greater virtues than logical analysis and knowledgeable discourse.

I don’t want to blow this out of proportion. I enjoyed Luke Skywalker’s decision to trust the force as much as anyone. But Luke’s decision was trusting his own coordination over that of a computer, not “trusting his instincts” instead of logic to make a decision. Popular culture has it that our brains should defer to our guts, despite conclusive anatomical evidence that guts digest food while brains digest information, and the success of the scientific method demonstrating that facts and logic are superior to instinct.

This week we wrap up our series on decision-makers. So far we’ve shot at lawyers, marks, zealots, and politicians. This week we’ll wrap things up with scientists and card players.

Given science’s inarguable success, you might think scientific decision-making is the way to go in business. There’s a lot to be said for it. Occam’s razor, for example — that among the explanations that account for all known facts you should always prefer the one requiring the fewest assumptions — is smart advice. So is the corollary that there’s always room for doubt, no matter how carefully you’ve tested a theory, because new facts may arise at any time.

But scientists can become as paralyzed as lawyers by the need for yet more data. While they understand that proof is impossible, they’re remarkably adept at envisioning what additional evidence might be gathered to reduce doubt even further.

Good card players avoid this paralysis. Consider the game of bridge, where much of the deck is hidden. While the bidding, the dummy, your own hand, and statistical probability all provide evidence of where the hidden cards lie, your information is limited. Even so, you have to decide how to play the hand.

It’s a good metaphor for the manager’s job — making decisions despite imperfect information, while taking into account every card that’s played (new information) to adjust tactics.

There are those who prefer poker or chess as decision-making metaphors. Let’s not quibble — as metaphors, each illustrates worthwhile principles.

The important point is this: Certainty is impossible, but you have to make decisions anyway. And while many figure uncertainty is the time to listen to your gut, they’re wrong.

Uncertainty demands the use of your brain. When your gastrointestinal tract talks, that just means it’s lunchtime.

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.