How can impaired reasoning affect a person with serious mental illness?

Some people with severe mental illness may have impaired reasoning due to their condition. People with thinking difficulties or muddled thinking may misunderstand the motives of the actions of their family, friends or others. This may result in all kinds of difficulties and misunderstandings, even provoking the person to self harm. Problems of thinking (called cognitive problems) are generally not very responsive to medication.
Family should keep communications simple and short and regularly express their regard for the person. Arguing about any misunderstandings may simply escalate difficulties.