Where the hedge is lowest, men commonly leap over.

Meaning: Temptation proves strongest where safeguards are weakest, inviting transgression.

Origin: Recorded in A Dictionary of English Proverbs and Proverbial Phrases, an undated collection published in London by Whittaker & Co. around 1880 and credited to Thomas Preston. Its earlier history hasn't been traced.

Equivalents in French, Spanish, German, Italian, Portuguese, and 3 more languages

French: Où la haie est plus basse on saute dessus (literally: Where the hedge is lowest men jump over)
Spanish: La ocasión hace al ladrón (literally: Opportunity makes the thief)
German: Gelegenheit macht Diebe (literally: Opportunity makes thieves)
Italian: L'occasione fa l'uomo ladro (literally: Opportunity makes a man a thief)
Portuguese: A ocasião faz o ladrão (literally: Opportunity makes the thief)
Dutch: De gelegenheid maakt de dief (literally: Opportunity makes the thief)
Russian: Плохо не клади, вора в грех не вводи (Plokho ne kladi, vora v grekh ne vvodi) (literally: Don't leave things lying about and lead a thief into sin)
Polish: Okazja czyni złodzieja (literally: Opportunity makes the thief)