A smile can have so many different meanings. A lot people think when someone smiles, this person is happy, positive and satisfied.
 I mean, of course, it can be true. Sometimes people try to cover their insecurity with a smile. Some smile because they are embarrassed. 

Some people smile because they just didn’t understand what someone else was saying. But some people smile to hide something. To hide pain, negativity, fears or problems they suffer with. Maybe for those people it’s easier to fake a smile than to be asked what is wrong. A smile is so much more than just a smile. 
Keep your eyes wide open and try to find out which kind of smile your friends are using. Because sometimes it isn’t how it seems...