In China, when trains open to allow boarding the crowd pushes forward.  
At first, I couldn't understand why people were in such a hurry.  After 
all, the seats are assigned.  Then I realized that some people have 
standing tickets.  Of that group, the earlier a person boards, the more 
likely he or she is to find an unoccupied seat and get to sit.  
(Obviously, if the person with the ticket for that seat arrives, the 
current sitter will have to move.)  It's Darwinian.  I guess the people 
with assigned seats board quickly at this time too (even though they 
don't have to hurry) is because of peer pressure and because they don't 
mind the crowd.