Instructions are usually clear and simple yet, no matter how bright you are I'm sure that there will be an instruction that you've either left out or one that you're not sure about.
For example the brightest of kid in class hands in there 50 page essay thinking that the larger the essay the larger the mark. Guess, again buddy, the instructions limit your assignment to 10 pages and now the student will get penalized by probably 15%.
Another example are page numbers and here i can say that I'm in fault. The simplest of instruction, all I have to do is click a button and 'poof' I've got page numbers. I think that when it comes to instructions, those that listen - that actually listen will follow instructions clearly and the outcome of their mark will determine that.
Moving away from educational instructions, you have normal day to day instructions which i believe is the hardest as you don't have someone to explain things to you. You will have to hope and pray that your reading the instructions clearly. Such as, when you need to warm pop - corn in the microwave although I know what to do as I have done this over and over I would read the instructions as I know the consequences.
Our behaviour to follow instructions will bring forth the outcome.