The ESV translation of 1 Corinthians 16:13 has Paul tell his audience to “act like men.” This tradition of translation goes back at least as far as the KJV, which renders the text “[behave] like men.” The NRSV, on the other hand, offers “be courageous.” What’s going on?
At issue is the Greek verb andrizomai. That word contains the root andr, which also gives us the word aner, “man.” (The “d” drops in and out, in accordance with Greek grammar. Aner is a “man,” and adres are “men,” for example.)
But the leap from the root andr to the translation “act like men” makes three mistakes.
The first is the wrong assumption that internal structure tells you what a word means. (I have more here: “Five Ways Your Bible Translation Distorts the Original Meaning of the Text.”) Relatedly, the root actually means “person,” not “man,” which we see from words like androphonos in 1 Timithy 1:9. The word phonos means “murder,” but androphonos means “murderer,” not “murderer of men.” (Similarly, “manslaughter” in English doesn’t only mean “slaughtering men.”) So we have methodological and factual errors.