Genetic testing decision-making for cancer predisposition is inherently complex. Understanding the mechanisms and influencing factors of the decision-making process is essential for genetic counselling and has not yet been investigated in Switzerland. This study's aim is thus to provide a theory about the individual's decision-making process regarding genetic testing for cancer predispositions in order to provide medical geneticists and genetic counsellors with insights into the needs and expectations of counsellees. We interviewed at-risk individuals who underwent genetic counselling in a clinical setting in Switzerland, using a grounded theory approach. Based on the interview data, we propose that a control-fate continuum, which is part of the individuals' life philosophy, importantly influences the decision-making process. Those in need for control decide differently compared with those leaving their future to fate. Several psychosocial factors influence the position on the control-fate continuum: "looking for certainty"; "anticipating consequences"; "being socially influenced"; "simplifying risks"; and "deciding intuitively vs reflectively". The control-fate continuum theory gives insights into the possible reasons behind decision-making regarding genetic testing for cancer predispositions. It includes both acceptors and decliners of genetic testing. Our theory helps healthcare professionals offering genetic counselling to anticipate problems within at-risk families and adapting their services to people's needs.