People can lose self-checking and to turn into crowd. 

The main property of crowd - she controls you.

Usually the crowd results from panic. 
Here the main thing for the person not to give in to the general psychosis and to keep common sense.
Do not give in to emotions, rely only on reason - he will prompt you right behavior.

Do not trust the crowd. Believe only what you see.
If do not agree with opinion of crowd, do not make aloud the observations. Read more about Survival in the crowd. The behavior at meetings, promotions, concerts