expression, godan verb (-ku)
take care of the penny; he who makes fun of one sen will cry at one sen
Proverb meaning that even a small amount of money should not be taken lightly; wasting or ridiculing a tiny sum can lead to regret when you need it. The literal reference is to the old Japanese sen (1/100 of a yen).
See also: 一円を笑う者は一円に泣く · 一銭
They say 'he who makes fun of one sen will cry at one sen,' so take good care of your small change.