If you and I were there, though, we should soon be out away behind, looking round the corner, and finding all sorts of odd places that unfortunately can't all get into the picture, only we know they're there, down yonder corridor, and from what the painter shows us we can invent the rest for ourselves.
One of the troubles of a painter is that he can't paint every detail of things as they are in nature.

A primrose, when you first see it, is just a little yellow spot.

When you hold it in your hand you find it made up of petals round a tiny centre with little things in it.
If you take a magnifying glass you can see all its details multiplied.
If you put a tiny bit of it under a microscope, ten thousand more little details come out, and so it might go on as long as you went on magnifying.
Now a picture can't be like that.

It just has to show you the general look of things as you see them from an ordinary distance.

But there comes in another kind of trouble.