Every day, all over Britain, people gather in groups to make decisions. Some big, some small, some important, some fairly trivial. The outcome could affect anything from the way a business develops to the route a new trunk road takes. It could create a hundred new jobs or add a hundred to the dole queue. And the really frightening thing is that most executives are happy if they get just 60% of decisions right. Which means they don't much mind if they get almost half the decisions wrong. Not surprisingly, governments and businesses waste billions every year making bad decisions. And often it's because the decision was made by a group.

In many areas of life there's such a thing as safety in numbers. For instance, when confronted by an unruly mob of away fans at a train station. But it doesn't really work when it comes to decision-making thanks to what leading psychologist Irving Janis rather imaginatively terms 'Groupthink'. Groupthink happens when you get together a group of people with very similar backgrounds, values and interests. Like a management board, for instance. People who either like or at least have a healthy respect for one another. Because of this, a consensus of opinion usually emerges when deliberating a decision and evidence to the contrary is automatically rejected. Sometimes even ridiculed. A slap on the thigh, followed by hilarious, raucous laughter and a knowing look usually do the trick. The bottom line is that individual members don't want to rock the boat because it might damage their personal relationships or even careers.

Experiments have shown that people are quick to adopt the majority position and, crucially, they ignore all the potential alternatives and all the conflicting evidence.

So what do you do about it if you want to make better decisions? Well, it's down to someone to make the group aware of the problems with the consensus view and offer alternatives. And as my good friend Alan Dedicoat, the Voice of the Balls, likes to say, it could be you. Someone needs to be appointed devil's advocate with the job of trying to spot holes in the decision-making process.

According to another leading psychologist in the field, Amiram Vinokur, a key part of this role is to nurture authentic dissent and mould it into constructive criticism. Because if mistakes are not spotted and dealt with in the meeting, they can be a lot more costly and difficult to put right at a later date.

Or to put it another way, if nobody is prepared to 'rock the boat' in the meeting, the boat will almost surely get rocked later. And often there are not enough life belts to go round.

Philip Hesketh is a professional speaker on the psychology of persuasion and author of Life's a Game so Fix the Odds.