Most women unconsciously seek an aggressive male mate. In women's DNA is a preference for a mate who will protect and provide for her and her children. Most women are naturally attracted to powerful and aggressive men who have proven to be successful.
Historically, both male animals and men have had to be aggressive in seeking a mate. One of the primary male hormones that helps in mating is testosterone. It makes males both "horny" and aggressive but men don't have to butt heads like some male animals do to get a mate. (That might be entertaining!)
However, men still need to show their courage and aggression in ACCEPTABLE ways to impress women. The man who can do his acceptable aggressive tactics best, has a better opportunity at getting accepted by the woman he desires.
Evolutionarily speaking, "civilized behavior" became fashionable only in very recent times, and men's aggressive acts for getting a woman's attention have become greatly restricted. Today, an acceptable aggressive act that gets a woman's attention is simply walking up to her with an "opening line." In most western countries this is acceptable aggressive behavior for men in public places like a bar, club, or dance hall. This action is usually not acceptable for women to do. That is just one of the many "unwritten rules" on flirting and dating.
Three emotionally powerful things are going on during this simple aggressive act men are suppose to do bravely when approaching a woman stranger with an "opening line". Guys, here is some of what is going on that makes your knees weak and shaky:
The old brain (i.e. the limbic system) is what controls our bodily systems such as heart rate, perspiration and breathing. As you approach the new woman, your limbic system will be running wild because of your ancient ancestors' experiences!
In some social settings it is acceptable aggressive behavior for a man to approach a woman stranger with an "opening line" to meet and talk with her.
Most western culture women really are attracted to the guy who can do it correctly.
There are fairly well defined rules for how to do this successfully, and the risks are high for failing.
Therefore it takes courage and an aggressive nature for a man to approach a woman stranger with an opening line. Some training is priceless for men new to the process of approaching a woman stranger. Researchers have identified a proven successful technique in common use, that is described next.