A soccer team can be thought of as eleven links in a chain. For a team to be successful, every link needs to be stable. Every player on the field needs to be confidently relied upon to do their job. If one player fails, the rest of the team has to shift and cover for them, subsequently not being able to do their job to the best of their ability. In other words, if one link in the chain breaks, the whole team can fall apart. In soccer, you are only as strong as your weakest link.
This “weak link” way of thinking can first be attributed to the book The Numbers Game: Why Everything You Know About Soccer Is Wrong by Chris Anderson and David Sally (I first heard about it personally through a podcast by Malcolm Gladwell — I recommend both the book and the podcast series).