I used to get mad because for so long my bosses and employers did not value the skill that I brought to the job.  The underlying philosophy that you are always replaceable- no matter how fast, clean, and impressive your performance- always bothered me.  I am UNIQUE! Reward me!  But really, I was going about it all wrong.  You must make yourself replaceable so that you can continue to move up the ladder.  You cannot be promoted unless there is somebody who can fill your shoes.  I am learning to not let myself hold me back.