I think the message is more "stop being so self-centered and overly sensitive and expecting everything to go your way and just get on with your life". If all you look for is "injustice" you will certainly find it under every rock.
I know, right? For example, as good as I am, and with all my positive qualities, there's this lady who heaps countless restraining orders on me . . . ~
While fairness sometimes equals justice ... the two are not always the same.
Some may think it's "unfair" that I am naturally gifted towards math, and didn't have to study it as hard as they did to get good grades. However, that doesn't make my grades "unjust" compared to theirs.
I'd say that it doesn't always mean that.. for instance, I say that a lot and what I mean by it is... don't feel bad, these things happen, and not just to you, you are not alone.. I am trying, I guess to empathise and say, I understand.
Depends on what context, if a parents had enough of their child going on and on, then yes it is said to shut them up. However, life being unfair is a good lesson to learn, and the reasons as to why it will never be fair, this is what drove people to fight for human rights, equal rights, women's rights, black rights etc. However, some of these fights have been meaningless if one doesn't accept some basic facts, such as the physical differences between men and women, or between races, shouting equal rights, without accepting a dose of fact and realism is nonsensical.