Just to give a bit more context, the full question I was originally asked is, “What if someone is a real introvert, and does not deal well with personal relationships or even being with people? Is it possible they don't have the capacity to handle relational circuits?”
That's a great question, and one I've wrestled through myself, since I'm an introvert. Here are some thoughts:
Having RCs on is not just about enjoying being around other people in an extrovert way. RCs can be on or off for introverts just as they can for extroverts, but there are different things that turn them on or off for introverts than for extroverts. I find that sometimes I'm overwhelmed by people and my RCs shut down, and being alone helps me get them back on. I can tell they're on when I feel content (rather than restless), when I feel centered and connected to myself (as opposed to stressed or numb), and/or when I'm able to settle into a sense that God is near (rather than that I have to work hard or beg to get him to hear and answer). Often this happens as I take a long walk outside or sit down with a good book. Then I can spend time with people again and enjoy it, and be in relational mode. I also know about myself that I'm much more likely to have my RCs on during a one-on-one or small group conversation than at a cocktail party or wedding reception, so I have to prepare myself to pay attention to my RCs more diligently when I'm at a big party.
So I would make a clear distinction between being introverted, on the one hand, and not dealing well with relationships and not having much capacity, on the other. Growing one's capacity and ability to deal with relationships in healthy ways can happen whether one is an introvert or extrovert, and it will look different for introverts and extroverts. For example, when my RCs are off and I don't want to talk with people, I just withdraw emotionally and come off as cold and uncaring, or anti-social. I avoid taking phone calls, I get annoyed when interrupted, etc. When my RCs are on and I don't want to talk with people, I can tell them graciously that I've hit my social limit and just need some alone time. I'll answer the phone and ask the person if we can set up a time to talk later in the day or week, and I'm able to set aside my work for necessary interruptions without grumbling about it - even when I'd rather keep working on a task. It's more about handling the situation relationally than about whether I'm naturally introverted or extroverted.
At the same time, it's quite possible, as you suggest, that a person may seem introverted because the actual issue is low capacity and their RCs shut down often or for long periods of time. Whether the person is truly an introvert or actually an extrovert who comes off as an introvert, they really need some help growing their capacity to be in joyful relationship mode. The best way to work on that is to start connecting with them as much as possible without overwhelming them. You can do this by noticing & telling them things you appreciate about them, attuning with them (listening well), and finding things that turn their RCs back on. These things can help build their capacity to deal with more difficult stuff. For some people this will take days or weeks. For others it will take years and a team of pastors, intercessors, therapists, family & friends. In the process, be careful not to overwhelm them, and be sensitive to the alone time they do want or need.
If you're involved in a relationship where the other person is like you described, I think your main tools are: prayer, keeping your own RCs on, and working on your own frustration and impatience as they arise. You might consider possibly having a frank but gracious talk with this person and offering help. It would also be valuable to find or cultivate a strong and joyful community for yourself that will work with you to love this person. You must also be willing to let the person make their own decisions about how to respond. It’s self-defeating to attempt to force or manipulate or nag someone into getting relational. That’s why prayer and doing your own internal work is such an important part of the process.