Almost all of the good things that have happened to me in my life were a result of managing and cultivating relationships. Most people get jobs through people they know. Opportunities are usually created through networks.
However, many people make the mistake of focusing on quantity rather than quality when they network. They think that having met someone now qualifies that person as a contact. Perhaps. But, meeting someone and leaving a lasting impression are two diffferent things.
For most of us, our careers are not significantly impacted by hundreds of personal contacts. Usually, it is just a few key relationships that shape the course of our lives. Next time you have the opportunity to meet or talk to someone, go out of your way to make an impression. Take an interest in your contact. Try and help them in some way. Following up with a timely, hand-written thank-you note will distinguish you from 99% of the crowd.