Counter-Intuitive Advice

Yesterday I read a piece of advice about working life that I immediately thought was completely wrong.
“Never make yourself irreplaceable at your job.”
It seems backwards.  I want to know that the company values my work and that they need to keep me around.  It makes me feel secure to think that if I take a day off work, they’ll feel the pinch.  That the cost of hiring a new person to do the things I do would just take too much time and too much money.
But then I understood.  Just the same that you won’t get fired, you also won’t get promoted.
then I thought about the people already at the top, the CEOs and Presidents out there, surely the same advice wouldn’t hold for them.  But it does.  If an irreplaceable CEO decides to retire, the repercussions to the rest of the company could be disasterous.  In this case having a replaceable CEO is good for all the employees.
It’s counter-intuitve because it feels so good to know that you’re valued enough to be irreplacable, but yet if you want to move up, it’s not the best position to be in.