Sometimes wisdom is the result of many painful lessons over a long life. Notice that Solomon doesn’t demand that his readers obey simple edicts, but offers his own experience. We happen to know that Solomon did have long experience with women — way too many of them. Given his huge harem, there is no reason to suspect Solomon ever chased an adulteress, but there’s no doubt he saw enough of it. His warning here includes the full range of his experience and observations together. Keep in mind this is also partly parable about idolatry, and just about any other moral folly that beckons.
Surely Solomon knew that legitimate wives could be trouble enough; no need to complicate things exponentially by borrowing someone else’s wife. If she’s willing to fool around, there is simply no way any good thing can come of it. You might as well sell yourself as a bond slave. By the time adultery is finished with you, there will be nothing left but pain. You’ll be old and have nothing to show for all the work an adulteress will make you do for her. What good does it do to berate yourself when it’s too late?
Solomon offers the image of slaking sexual thirst from your own well. He tweaks it just a bit by warning that it would be too easy to pour out all your drinking water into the public sewers. Consider that this is a somewhat drier land where water resources were so precious whole nations fought and were slaughtered for just a few wells. Treat your own wife as a precious fountain, a rare treat in that land. Stolen water cannot be as sweet.
Don’t be a fool; God is watching. He’s standing right there, reading your mind while you contemplate sin. If you are under a covenant with Him, you can be sure He will enforce it. It’s much easier to repent from things you only imagined you might do, than to clean up the mess from actually doing.