[jacquesm]

It's not so much the knowledge itself that has a half-life (unless it is front-end tech knowledge), but the ability to monetize knowledge. You used to be able to make a career out of some niche bit of knowledge but those days are over. You need to work hard just to stay current, in almost every field and that is as much a trend driven by technology as it is driven by the fact that there are so many people of working age now.

[jandrewrogers]

This is an excellent point. The frontier moves quickly, leaving a wake of commoditized skills behind it, but there used to be identifiable, well-paid skills that people chose precisely because the frontier moved slowly. While my instinct is to say that the frontier moves more quickly now, I have a suspicion that this less true than I think it is and what has really changed is that everything has a fast-moving frontier now.

For example, the evolution and development of the Internet technology in the 1990s occurred at an incredible pace that is as fast as anything I've seen since, but back then you could switch to being e.g. an Oracle DBA if you wanted to avoid the chaos, and many people did. Those safe harbors have become rare in tech and the relative pay for them declines every year.

[zelphirkalt]

This is why it is important to gain very good knowledge about the basics and "axioms" of whatever one works with. That way one can very quickly grasp "new" things, once it is needed. Without a solid grasp on the basics, one is bound to keep chasing the hype.

[zaptheimpaler]

Credibly signalling that you do have some bit of knowledge is hard too. Its easy to learn a lot on your own today but the only widely valid signals are academic credentials or past experience.