I get this question pretty often. The best answer is this one: you can’t. You can’t really convince someone with dementia that they have dementia.
Life would be a lot easier for caregivers if we could explain to people with dementia that they need help because they have a brain disease. Unfortunately, though, that’s not how dementia works. We can’t “convince” someone with dementia that they have dementia.
First of all, they probably won’t remember that you told them. And, most importantly, most people with dementia live in a slightly different reality than we do. Not only is it cruel to tell someone with a brain disease that they have a brain disease, but there is just no point—they aren’t going to believe you.
Here’s what you can do: work around them. A lot of caregivers ask me how to handle a loved one’s finances when they start to lose their own ability to do so. Instead of telling the person with dementia that they “can no longer do it themselves,” I suggest ways that the caregivers can work around that person, instead. For example, telling a loved one with dementia that you “want to automate the bills” so everything will be taken care of, or maybe that you want to hire a financial planner to help with sorting through everything.
It’s not a great answer, I know. The bottom line remains the same, though: you can’t “convince” someone with dementia that they have dementia.