The employees are often knackered after a day's work and just want to go home rather than hearing you go on about intransitive verbs. You might have an over-zealous training manager poking her nose into your lesson plans. You may be teaching in a conference room or small meeting room which is totally unsuitable. You may be faced with a group of students who should not be studying the course they've been assigned - that's either the fault of your language school for not testing the student's properly or the fault of the company training manager for having no idea whatsoever about the needs of his staff. So next time you go into a class with a textbook titled 'Advanced Business Letters Made Easy' and your class don't know the difference between the direct and indirect pronoun - you know who to blame.