It is their nature.

And, besides, it gives them pleasure to be mean and contrary this way.

They would die if they couldn't be villains.
They always save up all the old scraps of printed rubbish you throw on the floor, and stack them up carefully on the table, and start the fire with your valuable manuscripts.

If there is any one particular old scrap that you are more down on than any other, and which you are gradually wearing your life out trying to get rid of, you may take all the pains you possibly can in that direction, but it won't be of any use, because they will always fetch that old scrap back and put it in the same old place again every time.

It does them good.
And they use up more hair-oil than any six men.