The empirical study demonstrates, using the example of cooking and painting businesses in German-speaking Switzerland, that the subjective beliefs of vocational trainers can influence the quality of on-the-job training, which in turn acts as a protective factor against the termination of training contracts. This work thus provides new insights to better understand the professionalism of vocational trainers and the associated design of workplace training. Thanks to these insights, new measures can be developed to prevent the termination of training contracts.