If a father only taught his son one thing what should it be?

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So I think the 1 important thing is how to bed a woman while still a teenager. I think it's the key to a man's health and welfare. Nothing else is even close to that I believe. Coming from someone who has had problems with that all his life. Never taught from parents girlfriends or guy friends. I think that they all thought of it as a competition. I don't know why my mom never said anything.
If a father only taught his son one thing what should it be?
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