Help with my Java Moss please?

So, I've got my "little" tank, I'm not new to this, or I didn't think I was. I have always used silk plants until now, and I decided it'd be nice to have some real plants, so i did some digging and found Java Moss was "extremely easy" to grow. So I bought a small ball and wedged it between my rock and ornament. Then I waited. To my dismay instead of it growing rapidly, it died. What did i do wrong?