I don't think that could possibly be true unless you are yourself very limited in your cognitive capacity. Spending many hours with someone as their cognition is eroded by disease process, how can you help learning about the disease and the consequences? It would be like raising children and ending up not understanding more about developmental psychology. Not saying it will purge your thoughts of all mistakes, but you will learn a lot. Even simple things like the end of the day is a low point of cognition for dementia patients. The cycle between forgetfulness and poor nutrition. How the rhythms of conversation can last longer than the content of the conversations. How music can be a comfort when no words matter. How one can forgot one's children yet still have the ability to see if they are hiding upset feelings. The strange mosaic of skills and abilities that make up our full humanity.