Risky Shift Phenomenon. When people are in groups, they make decision about risk differently from when they are alone. In the group, they are likely to make riskier decisions, as the shared risk makes the individual risk less.
They also may not want to let their compatriots down, and hence be risk-averse. The overall tendency towards a shift in risk perception is also sometimes called choice shift.
There are a number of reasons as to why this might happen. Theories have included:
Myers and Bishop put highly prejudiced students together to discuss racial issues. They became even more prejudiced. The reverse happened with unprejudiced students, who became even more unprejudiced.
Entire football teams sometime get into aggressive or defensive moods as they either throw caution to the winds trying to score or desperately try to avoid being caught out.
Juries given weak evidence will become very lenient after discussion, whilst when given strong evidence they are likely to give harsh judgment.
Risky Shift Phenomenon
http://changingminds.org/explanations/theories/risky_shift.htm
Wallach, Kogan, and Bem (1964) proposed that greater risks are chosen due to a diffusion of responsibility, where emotional bonds decrease anxieties and risk is perceived as shared.
Collins and Guetzkow (1964) suggested that high risk-takers are more confident and hence may persuade others to take greater risks.
Brown (1965) indicates that social status in groups is often associated with risk-taking, leading people to avoid a low risk position.
Bateson (1966) suggests that as people pay attention to a possible action, they become more familiar and comfortable with it and hence perceive less risk.