I'm preparing a text for use in class, and somehow my brain isn't working. There's a German saying, "Gelegenheit macht Diebe", literally, "Opportunity creates thieves". What's the English equivalent? The text actually starts out with a play on words, "Gelegenheit macht Liebe", literally, "Opportunity creates love". The text is all about companies trying to forbid employees' dating each other. Can anybody suggest English expressions that capture the gist of the message?