There's many aspects of the rules that aren't explicitly written, it's the umpires job to interpret the document and try and apply them in the spirit of the game.
When does a push become a push, how long with the ball is an 'opportunity', what is a genuine attempt and so on.
That's the nature of the game, it's not tennis where it is black and white, it's a 360 degree, living, breathing contest of bodies.
Here's one for anyone confused about the out of bounds rule or being deliberately ignorant. This video contains two examples of one being not paid and paid correctly.
If you go to about 1.19 you see Selwood kick the ball and it goes out of bounds. His team is in front with not long to go and are trying to kill the game so if you were mind reading him for intent you would say he very likely wants the ball out of bounds. But there is a team mate close by so he has a legitimate option he was trying to execute instead of putting the ball out of bounds. So it's a throw in.
Just after that you will see Brayshaw kick the ball off the ground and it goes out of bounds. His team is two points down with 30 odd seconds to go and need to kick a goal and he is sending it forward. Again mind reading intent it is almost certain that he does not want the ball out of bounds. However the ball goes out without a team mate close by so he hasn't shown sufficient intent to keep it in. So a free kick paid.
I once heard an umpire give a really good answer to it at a presentation to the players, don't think of it as deliberate out of bounds, think of it as 'should have done something else' so the ball didn't go out of bounds.