Common knowledge is that information which most of the experts in a given field seem to know and agree on. However, if you ran across information that was unique to one or two of the sources, that would require a citation, even though you put it into your own words. You see, the idea is that then, even though you aren't giving credit for the author's words, you are giving credit for the author's unique ideas. And I've had students who plagiarized a sentence here and there from various sources. The former were quite deliberate.
Inadvertent plagiarism is still, however, plagiarism.
One is to study the statistics on the number of jobs that are going to be available in this or that category in the next ten years and base your life on that. That's following the rim of the wheel. If you do that, then you are up against your decision. You may not have a job, but you will have a life, and it will be interesting. You shouldn't study the statistics about the number of jobs that will be available in a certain field when choosing a profession.