Job Security - Where did they all go?

In class we talked about a series of jobs that are no longer relevant due to the advances of technology and, more specifically, the internet and the web. As for the main question of where did all the workers go, I don't really have that complex of an answer. I just believe they were forced to move onto to other things. Some likely moved into the very technological replacement that put them out of work, and some probably found other jobs. This got me thinking about the one thing that many people don't consider when looking for a career path; job security. Lets say you spend 8 years studying and working with everything there is to know about newspapers right before they become obsolete because of digital newspapers. It's kind of an obscure example, but in such a case you would likely move into digital newspaper production to further your career and to stay employed. If you instead work for a retail company as a cashier that completely moves all of its sales online, it puts you in a position of loss with nowhere to transition. For people in that situation, I just assume they found other work. The best case scenario would be a career that has its demand increasing. The next best would be a career in an area that, if it were to die, would at least have transition options. The case of my second example would be the worst case scenario. Although job security is sometimes very difficult to predict, it's something that needs to be considered to avoid that worst case scenario.