largeness of the task
A friend has agreed to be my guinea-pig -- to read critically the introduction of my book. She is largely ignorant of physics, which increases her value as experimental subject, because I want the introduction (if not the rest of the book) to be reasonably accessible to everyone, including people who know little or nothing of physics.
It is useful to be reminded that assumptions concerning physics, akin to those of Aristotle, say, are no dead letters, historical items, but can arise spontaneously, as good as new, in the thoughts of those who have not been schooled in the modern post-Galilean approach. Is it not obvious, for example, that the trajectory of a cannon-ball, fired out of the straight-line barrel of a cannon, will be qualitatively different (straighter) compared to the path of the cricket-ball, launched by the curved arm-swing of a bowler?
How many of these assumptions are there? Hundreds, thousands? I have no idea -- but they seem to go on for ever, and I include myself in this, as well as my guinea-pig