A proverb meaning that if something has happened twice, it is likely to happen a third time — used to warn or express caution.
彼が遅刻したのはこれで二回目だ。二度あることは三度あるから、今日は早めに連絡しておこう。
This is his second time being late. Since 'what happens twice will happen thrice', I'll contact him early today.
近所で同じ種類の盗難が二度発生した。住民は二度あることは三度あると警戒している。
The same type of theft occurred twice in the neighborhood. Residents are on alert, thinking it may happen a third time.