Peer pressure is a very powerful influence. As mentioned in a previous post, up to 80% of our brain is dedicated to processing social interactions and it uses 20% of our total energy to do it - more than any other human organ.
There have been many studies on the power of conformity in groups. One of the most well known is the Asch trials conducted in 1950s. In these experiments, groups of about seven people were briefed to give the incorrect answer to a simple question except for one poor unsuspecting victim. Over three quarters of victims gave wrong answers at some point (despite the correct answer obviously being "C").
* an asterisk at the end of a link means that if you click this link you will be taken to another site.