What makes a girl approach a guy ( stranger ) ?

I don't mean for hookups by the way... Is it because she finds him attractive and " safe " and he gave her the right vibes she doesn't get from most guys she meets? Is it mainly about the looks? Is it because he fits her type and she doesn't meet a lot of those very often? People ( including girls) say that girls don't do that with just anybody and I'm trying to understand it... Also because I often find myself in that situation with different types of girls so I wanna what's exactly the reason behind it...

What makes a girl approach a guy ( stranger ) ?
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