It isn't that hard.

It really isn't that hard to fake a smile when I need to.

You think you can tell when I'm upset, but I only let you see what I want.

When I'm really upset 

When I'm really hurt

When I get this uncontrollable urge to step off the sidewalk to become just another piece of road kill. 

You wouldn't know. 

I hide  it behind a real smile that I pull from a memory 

A memory from before I knew what it was to be sad

Before I could see through the curtained lies people told 

So don't think you know me, because I only let you see me sad to make you feel better.