I always make investment decisions by myself and not as part of a group. This is because there are some major problems with group decision-making.
One major problem is that it is likely to increase the confidence I have in an investment decision without leading to any greater accuracy in that decision (confirmation bias). This occurs simply because the group repeats a particular opinion. The more you hear a particular opinion the more likely you are to believe the opinion is correct.
Another major problem with group decision-making is that it can cause a polarisation of my opinions. That is I think that something is either right or wrong. An important part of my investment process is estimating the upside, central case and downside scenarios for a business and attaching realistic probabilities to those scenarios. If my views become polarised I may not attach realistic probabilities to these scenarios.
Yet another problem with group decision-making is that I may suffer from an information cascade. That is I may abandon my views on a business, and choose to agree with others in the group, because I think a group must know more than I do.
 P212, ‘Behavioural Investing’, James Montier, 2007.
 Ibid, P214.