When I use my key to connect to my AMI CentOS 6.3 server as ec2-user, it still asks for a password. Why?

When I use my key to connect to my AMI CentOS 6.3 server as ec2-user, it
still asks for a password. Why?

The command I'm using is:
ssh -i /<path-to-your-key>/<your-key>.pem
ec2-user@ec2-<your-domain>.compute.amazonaws.com
Why would it STILL ask for a password when i have the key? It has you
specify a key when you launch the instance; so if I use the key when I
connect, it shouldn't ask for a password. I have no idea what it is
because you're supposed to use the key to connect, right? What step have I
overlooked?