For improved motor skill acquisition, a successful skills curriculum should set training goals that motivate learners by providing a performance target. Proficiency-based simulator curricula set training goals based on expert-derived performance, tailor the training to individual needs, and have been demonstrated to produce uniform skill and improve operating room performance.4,5,32,33 Several authors have highlighted the advantages of proficiency-based training and the limitations of traditional time-based training (Figure 1).4,5,34- 39 While one study failed to demonstrate significant performance differences in the animal operating room between a goal-directed simulator-trained group and a self-directed group,40 additional study of better quality is needed to establish the advantages of proficiency-based training. Nevertheless, such training is limited by our incomplete understanding of surgical expertise.11 Who is the appropriate expert from whom to derive performance goals? How many experts are needed to create reliable goals? How many times should trainees perform the task at the expert level to have truly reached proficiency? Should we even use expert performance as a training goal or are there other more suitable methods? Are the available metrics the most appropriate for performance assessment and sensitive enough to distinguish subtle performance differences? If we do not understand who is truly an expert in a task, and if our metrics cannot capture subtle but important performance differences, the goals set for novices may be flawed and thus their learning may be incomplete. The traditional metrics of speed and accuracy used by most proficiency-based curricula may not be ideal for the measurement of superior performance,41 as they provide little or no information about what effort the performer invested or how much learning has occurred.10,42 Even motion-tracking metrics, which have proved valid for performance assessment on simulators and in the operating room,43- 46 have similar limitations.47 While 2 individuals may perform similarly based on speed, accuracy, and motion metrics, they may experience substantial differences in workload and attentional demands, which reflect differences in experience, true skill level, and learning.10,42 Importantly, incomplete metrics may impair the ability of simulators to confer the maximal skill to trainees. In a prior study,41 a visual-spatial secondary task that measured the spare attentional capacity of the performer proved more sensitive in detecting superior performance differences than the traditional metrics of speed and accuracy. Thus, incorporating these new metrics of automaticity42,48 into simulator training may help to better define and assess performance; this may have a considerable positive effect on trainee skill acquisition and learning. Such metrics may also help us determine the appropriate simulator training duration. Currently, most proficiency-based curricula require that trainees reach the proficiency level 2 consecutive times, an arbitrary amount of overtraining. Overtraining refers to the amount of additional training after initial proficiency is achieved that can positively affect trainee skill and learning.10 Because excessive training can lead to skill degradation,10 secondary task metrics may help quantify the amount of overtraining required to maximize learning by identifying the point of training where learning is complete. In a recent study,49 the application of automaticity metrics led to longer training duration of novices compared with the traditional metrics of speed and accuracy. On a practical note, expert-derived performance goals on the chosen tasks of the available simulators should be established and provided to residents as training goals. Such goals that are usually based on speed and accuracy/errors (±motion metrics) can be found in the literature for most laparoscopic simulators, but could also be established using local experts and previously described methods.14,50,51 In addition, trainees should be required to achieve these goals on consecutive attempts (2 are used by most authors)4,32,37 and perform a number of additional repetitions (5-10) for reinforcement. As mentioned, these requirements need further study, and additional metrics may be needed for optimal performance assessment.