18 To Enoch was born Irad, and Irad was the father of Mehujael, and Mehujael was the father of Methushael, and Methushael was the father of Lamech.
19 Lamech married two women, one named Adah and the other Zillah. Genesis 4:18-19
Here we see Lamech departing from the norm by marrying two women. At least it’s the first recorded instance of it. By him having two wives, we can already tell he marches to a different drummer, something we’ll continue to see a bit later. Doing things differently isn’t wrong if it stays within God’s moral code.
You could make a case that all of the Old Testament prophets did things a bit differently than the people around them, but generally they were speaking on behalf of God so their moral code was directly in line with His. How they proclaimed their message was always different, but the message was the same.
Lamech probably figured out that two wives were more than he could handle. It was never God’s intention for man to marry more than one woman, and vice versa. God put certain rules in place to protect us from unnecessary pain and grief. Monogamy with the opposite sex is one such rule. When we stray from that Godly norm, we risk hurting ourselves, others, and society as a whole.