Achieving an ambitious goal frequently requires succeeding in a sequence of intermediary tasks, some being critical for the final outcome, and others not. Individuals are not always able to provide a level of effort sufficient to guarantee success in all the intermediary tasks. The ability to manage effort throughout the sequence of tasks is therefore critical. In this paper we propose a criterion that defines the importance of a task and that identifies how an individual should optimally allocate a limited stock of exhaustible efforts over tasks. We test this importance criterion in a laboratory experiment that reproduces the main features of a tennis match. We show that our importance criterion is able to predict the individuals' performance and it outperforms the Morris importance criterion that defines the importance of a point in terms of its impact on the probability to achieve the final outcome. We also find no evidence of choking under pressure and stress, as proxied by electrophysiological measures.