Why do more educated workers experience lower unemployment rates and lower employment volatility? Empirically, these workers have similar job finding rates but much lower and less volatile separation rates than their less educated peers. We argue that on-the-job training, being complementary to formal education, is the reason for this pattern. Using a search and matching model with endogenous separations, we show that investments in match-specific human capital reduce incentives to separate but leave the job finding rate essentially unaffected. The model generates unemployment dynamics quantitatively consistent with the data. Finally, we provide novel empirical evidence supporting the mechanism studied in the article.