Many will have noticed the phenomenon whereby some people make negative comments about other people but these reproaches also happen to be true of themselves who are verbalising them, e.g. someone saying of another they cannot deal with being challenged or being disagreed with when in fact this is also their problem.
I do not think this is due only to hypocrisy but to the fact that it is harder to see oneself objectively than it is other people, perhaps because others are external and farther away from us and that, as philosopher Heidegger knew well, the most arduous task for human beings (whom he refers to with his German concept of Dasein) is to see and understand what is closest to them.
And what is closer to human beings than their own soul?
In addition making comments about others that apply just as equally to oneself could be symptomatic of the now overused but still relevant insight that
"it takes one to know one."This can result in the accusation of projection, i.e. that in criticising another we are merely projecting our own insecurities or value systems onto this other without understanding where they are coming from or the difference in wavelength that may or may not pertain.
In that respect it could also be said that
"it takes one not to know one."