Courses and books are pathways that converge to the same truths. Missing a lecture or skipping a chapter does not mean a piece of knowledge is lost forever. It means you will arrive at the same truth through another path, eventually.
The bias is the nagging guilt that any gap in the curriculum is an irreversible loss. It makes you re-read chapters you half-remember, restart courses from the beginning, and treat the table of contents as a checklist rather than a map. The truth is that ideas are bigger than their representations. Two different textbooks, two different teachers, two different life experiences can all lead to the same understanding.
The right thing to do is not to chase completeness, but to think hard about what truths hide behind the particular representation you have in front of you.