I think that insight impairment can be an aspect of dementia where the sufferer isn't aware of their cognitive loss.
Some people are aware that their memory, problem solving and other cognitive skills are becoming impaired. They may attempt to hide it from loved ones and even may deny it to themselves but there is awareness. They will attempt to cover up failures and may get angry with people who attempt to discuss it. Where insight is impaired the sufferer will genuinely be unaware that their behaviour has changed and is now unsafe or unusual. They will not be bothered about hiding it and , while they may get angry if challenged, they will be genuinely puzzled aboit why people are concerned