If someone is being a dick and doesn’t realize why they’re being a dick

I think you’re confusing the words “how” and “why”. Why they’re being a dick is a question for a therapist, unresolved childhood trauma, insecurities etc.

How they’re being a dick is the question you seem to be referring to. They don’t realize that what they’re doing is wrong or hurtful, because they don’t see how their actions are affecting their partner.

“How does that make you feel” is another good question. I might be unaware that my actions are upsetting in the first place.

But saying “why do you feel that way” creates separation between yourself and your actions and places the burden of introspection on the partner, not yourself. My partner gets upset when i make a mess, because I made a mess. Their feelings do not require introspection. My actions are the issue in that case. If im confused i would ask “How do my actions affect you?”. I might not realize how big a problem the mess is for them, that’s where the education is needed, not on why they have feelings about my mess.