when it comes to big companies, they should have separate teams for the front end and the back end, and more often than not, they might have more detailed division in each field, like a smaller team is responsible for the database only. things might change with the changes of IT, especially when cloud is becoming more and more popular. but when it comes to small companies, or independent developers, very probably they should know all of them, though they need not to be experts in every field, large or small. actually, it seems more and more popular even to middle and large-sized companies, which is why Full Stack Developer becomes a hot topic recent years.
to a beginner, it might be a good thing as he should know what is supposed to do and which direction the trend is coming from and moving forward. i don’t know, maybe it’s just like anything else from technical perspective, it has different levels to any field. to the so called Full Stack, there are also junior, senior and experts, etc. for example, we can build up a blog website, which is a beginning of this as that means we know something from both the front and back-end, though probably not much. but it’s ok, with more knowledge to some front-end languages, like HTML, CSS and JavaScript, and those of back-end, like php, and even more knowledge of the system kernel, we are more advanced in this field and can do much much more.
it might take time and energy, but that is how it works, and as long as we carry on, it will pay off, finally.