You have to decide what is extraneous and what is central. There is always more to tell. If you want to have a finished product, at some point you have to say "enough."
You will never get to the irreducible definition of anything because you will never be able to explain why you want to explain, and so on. The system will gobble itself up.
How did you get back?' asked Vautrin. 'I walked,' replied Eugene. 'I wouldn't like half-pleasures, myself,' observed the tempter. 'I'd want to go there in my own carriage, have my own box, and come back in comfort. All or nothing, that's my motto.' 'And a very good one,' said Madame Vauquer.