When do you know the employee isn't going to learn the task properly? How long should you give it?

New employees should be trained properly at the commencement; this is the time to observe and spot errors being made and correct them. While each employee learns at their own pace, the amount of time to give them should depend on how much experience they promised you they had in their interview/CV combined with the average time your industry expects the person to come up to scratch. The harder the task/knowledge, the longer the time needed. The most telling signs an employee isn't working out include ongoing incompetence, reticence to ask questions when stuck and passing tasks off to coworkers frequently.