Why do you think men find it hard to approach very confident women?

And I'm not talking about insecure men as such because I see relatively confident men that show all the signs of wanting to take the next step that goes beyond simple flirting but a lot of the time when it's time to move to the next step they never do for reasons that are unknown. And I wonder why that is? Especially if the confident women in question responds positively to the flirt.
Why do you think men find it hard to approach very confident women?
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