Is there are separate rule (or phrase/idiom) one can quote for the "Serial Programs" part of Amdahl's Law? This is one area where teams waste a lot of time; sp

Is there are separate rule (or phrase/idiom) one can quote for the "Serial Programs" part of Amdahl's Law? This is one area where teams waste a lot of time; spending too much effort improving an area which doesn't matter so much. Amdahl's law could be quoted, but the articles generally skew heavily towards parallelism.