It has been said that idleness is the parent of mischief, which is very true; but mischief itself is merely an attempt to escape from the dreary vacuum of idleness. George Borrow
When children are doing nothing, they are doing mischief. Henry Fielding
O mischief, thou art swift
To enter in the thoughts of desperate men!
William Shakespeare (Romeo and Juliet, 5:i)
For Satan finds some mischief still
For idle hands to do.
Isaac Watts
There are but very few men clever enough to know all the mischief they do. Francois duc de La Rochefoucauld