a small-minded person being idle tends to do evil
Proverb and yojijukugo, often cited as part of the longer phrase 小人閑居して不善をなす. Used to warn that idle hands are the devil's workshop, especially for those of weak character.
See also: 小人閑居して不善をなす
There is a saying: 'A small-minded person, being idle, will do evil.'
彼は小人閑居の典型で、暇になるとすぐ悪さを考える。
He is a typical example of 'a small-minded person being idle'; as soon as he has free time, he thinks of mischief.
The full proverb from which 小人閑居 is derived. The shorter form is often used as a standalone yojijukugo with the same meaning.
Derived from the classical Chinese text 'The Great Learning' (大学). The phrase originally warned that a person of low character, when idle, will engage in wrongdoing. The shortened four-character form 小人閑居 is used as a yojijukugo in Japanese.