Confidence matters because:
1. Women want you to offer and them to chose. This saves them any embarrassment of saying what they want.
2. Women care about more than just your looks. If you act less confident than your appearance, they will think you have a small dick or something. If you are over confident, they may assume you have something else to back it up.
3. Wome use men. If you let on that you doubt your worth, they will try to get more from you for less. Why have one guy take her to the moves once a week when she can go 3x because two guys are too shy to ask for more than just friends, but will pay anyway because they don't think they can do better? Show doubt, and they will eat you alive.
4. Dating is like a job interview. If you don't think you are good enough, neither will they. If you are willing to work for less, they will gladly pay you less. If you ask for too much, they will either expect more work, or just not hire you.