>Don't be irreplaceable. If you can't be replaced, you can't be promoted.

I think it depends whether you want to be promoted and where you want to be promoted to.

>Here at where I work we used to have people the wouldn't share their knowledge thinking they had job security then. I personally don't believe anyone isn't replaceable. It might hurt for a while but someone still step up or you might learn that you didn't need that information in the first place.

I agree. It is all a matter of cost and time.