The other side of this is that I've met several people over the years who were true world class experts in their fields (one literally wrote the book, the other

The other side of this is that I've met several people over the years who were true world class experts in their fields (one literally wrote the book, the other had her phd in that niche, the third was employee #5 at the company, etc...) where suddenly those entire fields went poof as technology changed. So this is the tradeoff - do you specialize and potentially then have to shift in some new direction as the world change, or do you remain more generalized and thus sometimes have a harder time selling yourself?