That's quite a good analogy. Except that while you're colouring in, there are other people also colouring in the same picture, all at the same time. Some of them aren't very good at colouring in.
Sometimes a guy will colour up behind you with a big expensive pen, and generally colour like a bit of a dick, because he spent £100k on his pen, so that gives him the right to colour however he likes. So he scribbles all over all of the lines - he just wants to colour as fast as he can, to show off his pen.
Also, you have old grannies, who are using pens which really should have been binned years ago, and are colouring in at a speed that really hinders other colourers around them because they can't really see the colouring book very well.
And as mentioned, you might have someone who is only half concentrating on the picture at hand, and is colouring in with one hand while glancing at their phone in the other.
Some people suck at colouring and shouldn't be given a pen license at all.