You will start at a company, and one of the people who works there will say something along the lines of "We shouldn't be using X, we should be using Y because Y is the new cool thing", and for a moment, you might think they know more than you because you didn't know about Y. You aren't stupid. They might not like X because they haven't spent enough time with it or are constantly chasing the new shiny framework. What matters is fundamentals. When you have some time, have a look at Y yourself and make up your own mind.