A chain is only as strong as its weakest link

A chain is only as strong as its weakest link

A chain is only as strong as its weakest link" implies that it does not matter how strong a team is, if they have a member that can be exploited in weakness, then they will all fall. That is why we need to "cover all the bases" and not only prioritize a number of things. We need to be stable in all aspects as to not fail easily. In experiments, the data you gather is only as significant as the worst of your findings, since the validity of the experiment relies on all the stats combined. I think that is what your teacher is talking about.