The goal–performance relationship is strongest when people are committed to their goals. Seijts and Latham (2000a) found goal commitment questionnaires to have high reliability and validity. Commitment is most important and relevant when goals are difficult (Klein, Wesson, Hollenbeck, & Alge, 1999). This is because goals that are difficult for people require high effort and are associated with lower chances of success than easy goals (Erez & Zidon, 1984).