"I remember in my childhood, when we argued in the courtyard, we used to say: it takes one to know one. That’s not … just a children’s saying or joke."

"We always see our own traits in other people and think they are like how we really are. And as a result we assess [a person’s] activities and give assessments."

Said Vladimir Putin, quoted in "'Takes one to know one': Putin-Biden spat escalates after 'killer' accusation/Officials in Moscow go on offensive after Biden says Russian president will pay price for election meddling" (The Guardian).

Putin added, ominously: "I would tell him: Be healthy. I wish him good health. I say this without irony, without joking."