Person is expected to perform unaided. Task is infrequently performed. Task must be learned as a prerequisite for higher level tasks. There are multiple steps or attributes. Steps must be performed quickly or smoothly.
Safety is critical, no margin for error.
Situations are novel or unpredicable. Task is simple and job turnover is high. User lacks the reading, listening or visual skills to use a job aid. Users are unavailable or lack time for training. Task is perceptual, unable to develop a useful job aid.