The reason these sequences of commands always start with cat, for me at least, is that I just cat’d the file only to find it was too long or noisy.

    cat filename.txt 

    Up | grep “thing I want”

Is fewer keystrokes than

    cat filename.txt

    grep “thing I want” filename.txt

Or more likely

    cat filename.txt

    grep filename.txt “thing I want” 

    grep “thing I want” filename.txt