In a real effort experiment with repeated competition we find striking differences in how the work effort of men and women responds to previous wins and losses. For women, losing per se is detrimental to productivity, but for men, a loss impacts negatively on productivity only when the prize at stake is big enough. Responses to luck are more persistent and explain more of the variation in behavior for women, and account for about half of the gender performance gap in our experiment. Our findings shed new light on why women may be less inclined to pursue competition-intensive careers. Keywords. Labor market outcomes, gender gap, experiment, real effort, career development, competition, luck, productivity, relative performance evaluation, tournament, winning, losing. JEL classification. C91, D03, J16.