Previous research has suggested certainty to be an important factor when investigating effects of level of expectancies on future behavior. With the present study, we addressed the interplay of expectancy certainty and level of expectancies regarding task performance. We assumed that certain performance expectancies provide a better basis for the regulation of persistence and, therefore, lead to improved performance when people expect to perform well. However, when people have bad performance expectations, being certain (compared to being uncertain) about this expectation decreases motivation to work hard on the task because it is assumed it will not pay off anyway. Accordingly, in our study, we found that the performance of participants with high performance expectancies increased with increasing expectancy certainty. By contrast, performance of participants with low performance expectancies decreased with increasing expectancy certainty. Additionally, certainty and expectancy were shown to be unrelated, supporting the idea that they are independent constructs.