I first read these words in the window of a shop down a side street in St Ives and they struck me then, as now, as being a very wise principle by which to manage one's possessions.
I am, by nature, an inveterate hoarder, the result of which is a cluttered house. Friends are kind enough to say it looks lived in but I know it's often a mess. Not only is it difficult to keep clean but it's also a terrible waste of stuff that would be better off elsewhere.
Lately I've been attempting to 'downsize', in other words, get rid of stuff. It's not always easy but there is a real sense of liberation in filling a charity shop bag and carrying it out the front door.
The other side of the equation is attempting not to acquire any more stuff to take its place. This is harder but William Morris' maxim might help.