In this article, we present a new mathematical function, called systemability, by introducing the uncertainty of the operating environments as a random variable for predicting the reliability of systems in the field. Industrial manufacturers must deal with problems of how to predict reliability performance of systems during operating conditions in various applications from the customers' perspectives. The authors recently introduced a new model, called systemability, which appears very interesting and suitable for industry applications, because it separates the effects related to the machine components from the environmental factors. After a brief literature review, we discuss the use of systemability function to predict the reliability of the system in the field. In this article, the adequacy of systemability model that fit the observed real-world data of the two applications, in the automatic packaging machines for beer production and the motorcycle system, has also been assessed. At the end, the results are shown and also discussed.