Picture if you will for a moment, a doctors office. A husband and wife sit across the desk from the doctor and he has just told them that the wife has cancer. She will need surgery, weekly doctors visits, daily medication and he is not sure if the cancer is curable. This will be a long road for the couple. Then the doctor turns to the husband and says "You have a lot going on right now with work and managing your diabetes, there is no need to let your wife's issues add to your difficulties."
Now, you may not think that this doctor is all that compassionate or understanding. He basically told the husband that his wife's cancer is her illness alone and he should not be bothered with caring for her. You may think advice like this does not happen often, but it does, at least for caregivers of people with mental illness.
I talk to people all over the country who are caring for a loved one with mental illness. Parents, siblings, partners, friends. The advice above is a fairly common from some people in the helping professions (ministers, counselors, therapists). I think is unhelpful at best, damaging at worst.
This advice is some form of: "Do not take on someone else's problems" or "You have enough going on in your life already, there is no need to let (your partner, child, etc...) add to your difficulties."
I understand that this is well meaning, as a way to help the caregiver put up some boundaries and make sure that they care for themselves in the midst of helping another person. This advice can also sometimes mean that as a caregiver you do not take on your loved ones insecurities, insulting behavior, or irrational thinking, if they have any of those symptoms. (By the way, having mental illness does not mean everything we do is irrational).
While the advice is well intentioned, it also comes with a whole lot of assumptions, stigma, and judgement. In fact, it is advice that I am pretty sure you would never give to a caregiver of someone with any other illness.
This advice, given mostly to caregivers of people with mental illness, assumes that mental illness is a choice. It assumes people with mental illness are just trying to make life difficult for others and that they are inconsiderate. It assumes that we have no community responsibility to care for people with mental illness, because they bring it upon themselves. This advice leads to caregivers loosing compassion and empathy for their loved one.
So, what can you say instead to get the message of self-care and boundaries across and not use a phrase that stigmatizes mental illness? How about something like: "Make sure to take care of yourself as you care for your mother and if you need help and are overwhelmed, ask for help." Then brainstorm a list of people they can ask for help when they need it. Or say: "I know your partner is saying unkind things to you, which is inappropriate. You do not need to take on their beliefs about your as your own." Suggestions like these do not assume the person with mental illness is a burden who has chosen to be a burden, and whom the loved one (who willingly entered into a relationship with this person) has no responsibility to help care for them. It is also a big assumption to think that the caregiver has no bad behaviors which might be exacerbating the situation, so don't blame it all on the person with the mental illness. You really need to look at the whole system to give good advice.
Often people argue with me that "If someone has mental illness and they have bad behavior, that is an extreme situation and unlike anything else, so you need to just walk away." Untrue. I hear couples all the time who treat each other terribly. Neither has mental illness, but they yell and scream at each other, they blame and shame. Parents call their kids "irresponsible brats" and make them feel unworthy. Parents feel overwhelmed at the daily caretaking of their kids. People with all sorts of other illnesses have bad days where they lash out at their loved ones caring for them. This is all about managing communication and environment to enable the best relationship possible so that the person with mental illness is cared for and loved and the caregiver is not burnt out and they also feel loved.