"The things that we want we willingly believe, and the things that we think, we expect everyone else to think"
- Julius Caesar
Herd behaviour, the bandwagon effect, social proof, call it what you like, but used well it is a highly effective process which can be utilised to influence people to move towards a desired position on a particular issue.
Most people have a need to be well regarded by others, and as part of that need they feel that they should be seen to have a point of view on important issues. The problem is that people are often unable (or unwilling) to put in the effort required to investigate the various aspects of an issue in order to arrive at a totally independent assessment. As a default, they often adopt what they see as a 'safe' option, by expressing the view that is perceived to be held by most other similar people.
The process of social proof explains a lot of the shifts that occur in public opinion. Published surveys that show how most people are thinking on an issue can of themselves actually influence the opinions of those who are not strongly committed. Of course, there are limits to the extent to which changes of mind will occur, and it is important to firstly define the boundaries around which people give us 'permission' to operate.