To be idiomatic when speaking another language, that is. Here's an example I ran across today at the Easy German website:
It's far more idiomatic English to say, "Germans can be rude sometimes." Whoever wrote that was thinking in German but writing in English. The German would read, "Germans can sometimes rude be."
A famous example of what I'm talking about is the German tourist in the U.S. who told his server at a seafood restaurant, "I've been here since an hour. When do I become a fish?" He meant, of course, "I've been here for an hour. When do I get a fish?" But he was thinking in German, not English: "Ich bin hier seit einer Stunde. Wann bekomme ich einen Fisch?" Close, but no cigar.
I tell my Greek students that the goal of learning Greek is, to a degree, to be able to think in the language and not merely to translate Greek into English. That's why we work on English to Greek sentences. Hard? Absolutely. But indispensable!