That comment about how unproductive he was standing against the wall, he referred to it later in his book of Cox's rants and how much it hurt him emotionally 😂
Dr Cox cares about JD because he saw potential in him, so he goes hardest on JD more than the other doctors. he knows JD is sensitive and acts dumb but deep inside that layer of marshmellow is a smart and hard nosed doctor who will save lives one day. Cox won't allow JD to fall victim to self doubt, pity, emotions etc because as a doctor you have to focus on the treatments and make the right diagnosis. Cox was a hard ass but for good reason
Taking emotional/parenting advice from someone like Cox - lol. And to me he's kind of like the author's voice in this show, too, which is just no good. Allowing yourself to feel the emotional damage is how you can overcome it and learn to not repeat it.