Libra likes balance. Capricorn likes control. Both are cardinal, signs which are known to be controlling. Mercury rules communications. I remember watching an episode of M*A*S*H* where Hawkeye and B.J. squared off, each needing the last word. I remember thinking, “Hey, that’s me!
I have a 7th house (Libra’s house) Mercury and like a balanced exchange. I seek balance in my conversations in general. That tends to work out just fine most of the time, unless I am talking with someone who is also of this ilk. Then it can go on and on and on. I also have a Capricorn Moon, a Saturn-ruled Moon that needs to have things settled. It’s in sextile to my Mercury. Probably the kindest thing someone can do for me in this regard is to tell me it’s all right to not reply. That is a relief (Moon).
This is the kind of self-realization that can be uncomfortable at first, when you realize you are so controlling that you feel out of control. However, self-knowledge is helpful in the long run, particularly when it comes to control. You can always make the decision to control yourself. You can decide to balance by allowing someone else the last word!
Do you need the final word? Where is your Mercury?