Forming therapeutic relationships is considered important within psychiatric and mental health nursing. One way of achieving this is through social interaction when engaging in joint activities. However, introducing and using nursing interventions based on joint activities in psychiatric inpatient care has proven challenging. Since staff motivation is important, researching the meaning of engaging in joint activities from the nursing professional's point of view can provide information that is relevant in this area. This study aims to illuminate the meaning of participating in joint activities with patients as narrated by nursing professionals in psychiatric inpatient care. Narrative interviews with 14 nursing professionals with experience from psychiatric inpatient care were conducted. Data were analysed using phenomenological hermeneutics and reported following the consolidated criteria for reporting qualitative research (COREQ) guidelines. Results illuminate that engaging in joint activities means being open to a process of learning. Four themes contributed to this understanding: Struggling with uncertainty, discovering aspects of the other, unfolding paths to self-fulfilment and sharing personhood. Being open to a process of learning means being willing to face uncertainty when engaging in activities as well as being open to learning about oneself as well as the other. Through openness to this process of learning, a sharing of personhood can be achieved, where the nursing professional and the patient approach becoming two persons. Illuminating the meaning of joint activities from the nursing professionals' perspective may provide valuable insights related to introducing and using interventions focusing on joint activities.