a small leak can sink a great ship; small matters lead to great consequences
Proverb warning that seemingly trivial things can cause major problems if ignored.
As the saying goes, a small leak can sink a great ship, so you must not overlook even small mistakes.
A Japanese proverb composed of 小事 (small matter) and 大事 (great matter), literally 'small things are big things'. The exact origin is uncertain, but it reflects a common cautionary theme.