I don't know how many times I've heard it throughout my life. Someone who's relatively comfortable in their circumstances telling someone who isn't, that life is not fair. Sort of like telling them to "get over yourself" in a condescending manner. "Pull youself up by the bootstraps". To me, that's VERY cold and thoughtless.
My take on it is that most often people are not fair to each other. That's the only reason poverty exists. That's the only reason discrimination exists. It's the only reason people are left to wander the streets without a place to lay their head. A lack of compassion and empathy.
As a small child I can remember feeling this way, and it's stuck with me all my life. In fact, just thinking about needless suffering can bring me to tears. There's a helplessness attached to it. What can one person do to make those around them see that people hurt people in a much larger way than circumstance does.
"Life is not fair". Think of those words. What's REALLY not fair is that most people just don't give a fuck about anyone but themselves.