New product sales are hard to predict. Our analysis of sales performance two years after market launch reveals that three groups of factors do not increase the accuracy of predicting new product sales: (1) A firm’s general experience and experience with innovation; (2) High technological competences and strong knowledge networks; (3) Customer involvement in new product development. R&D managers should realise that experience with innovation as well as high technological competences, while possibly helpful during the development stage, do not necessarily enhance an accurate prediction of new product sales. Moreover, other than intuitively expected, networking can be ambiguous: It reduces uncertainty about future sales performance by providing information; but it may also enhance knowledge leaking to competitors, thus increasing probabilities of unexpected failure.