It really has nothing to do with how big you are. And no you don't need roids.
It's about being healthy. Being healthy is natural. Lifting weights and eating right pumps you full of testosterone and THAT is what gives a man his ambition, his drive and his purpose in life. Healthy men are full of testosterone. They go after the education they want, they go after the types of jobs they want and they go after women. Men wanting women and women wanting men is NATURAL and healthy. Sex is natural and healthy and the more healthy you are, i.e. in shape, eating the right foods and having ambition, the more naturally all of this stuff comes TO YOU. To me, this all started when I started lifting and eating right. That Testosterone that you'll get is what will make your life complete. So there isn't a certain size you should be aiming for. What you should be striving for is making your mind and body strong and for a-lot of guys this is based around living a healthy life, again, eating right, staying in shape, etc. THIS is what will give you your ambition and drive in life.
You asked me for some examples of how I've seen this play out in my life. Specifically when it comes to women, it's made things easier. I still have to put the effort in and I still get rejected but the women who I do date and have sex with are animalistically drawn to me. Sex is much more passionate and intense. They naturally enjoy my leadership in the relationship and they naturally want me to lead. This is all natural and healthy and it's because I AM a healthy man. I am sound of mind and body and AGAIN this all started for me in the weight room and by eating right. Don't aim for a certain size or shape, just start lifting weights and eating right and your life will magically transform itself. You will start going for want you want in life (jobs, education, women, opportunites). It all starts with testosterone. It's hard to explain, but this post by POOK is a great way to break it down:
http://www.sosuave.net/forum/threads/the-secret-of-the-jerk.17008/
Do read that post over and over again until it sinks in. Sorry if I didn't explain it well enough but hopefully that article will.