Relatives are increasingly recognized as important in the care of people with a serious mental health condition, such as major depressive disorder, bipolar disorder, or schizophrenia. Research indicates that in providing care, relatives use so-called treatment pressures, such as persuasion, interpersonal leverage, inducements, or threats, to promote the treatment compliance of their family member. This grounded theory study investigated why relatives use treatment pressures by analyzing the experiences of relatives of people with a serious mental health condition before, during, and after mental health crises of their family member. We conducted 11 semi-structured, problem-centered interviews with such relatives in Germany between October 2019 and January 2020. Our analysis showed that the key category of relatives’ experiences is a predicament characterized by feeling responsible to take action while experiencing a limited range of action. Relatives’ perceived responsibility to take action had three dimensions: relatives’ worries about their family member and other members of the family, societal norms and expectations, and the transfer of responsibility from the mental healthcare system to relatives. The limitation of relatives’ scope of action also had three dimensions: their family member’s opposition to treatment, legal criteria for involuntary commitment or treatment, and their dependency on mental healthcare professionals and the mental healthcare system. We reconstructed three different ways in which relatives may deal with this predicament: assuming responsibility for their family member’s treatment, which involved exerting treatment pressures, staying out of their family member’s mental health–related matters, and focusing on their own well-being.