You get the offer letter and feel a surge of hope. After a few rounds of negotiation, you take the job. You're happy and optimistic, as are your new co-workers and managers.

If it turns out to be a good fit, you'll feel challenged, rewarded, engaged, and even happy on the job. Even the frustrations will feel fruitful, because you're a top performer and don't want it to be easy.

But is the job serving you in creating the life you want? Are you thriving because you are working here, or is there something at the edge of your consciousness that doesn't feel quite right?

If you're not personally thriving even though you have a good job, it may be because there are some unseen forces at work. I don't mean ghosts or wizards--I mean something called social contagion. It's a powerful, mostly hidden force that exerts a powerful influence on our well-being.

Three Degrees of Separation

In 2007, sociologists Nicholas Christakis and James Fowler proposed the idea of social contagion to explain the data coming out of various studies they were conducting.

Social scientists have known for years that if one spouse dies, the survivor's risk of death can nearly double. But Christakis and Fowler demonstrated that this kind of secondary impact was at play in all relationships and could predict more than just mortality.

What they were able to show is that the social networks we occupy exert a powerful influence on every aspect of our lives, including the levels of success and stress we experience in our careers.

In one study they found that if your friend becomes obese, your chance of becoming obese increases by 45 percent. But it doesn't stop there. If your friend's friend becomes obese, your likelihood of obesity increases by 25 percent.

This is true even if you never meet or even know of the existence of this second-degree connection. It's a nonconscious influence that flows through a social network, operating beyond our control and perception.

The impact diminishes dramatically after three degrees of separation, but it affects all kinds of outcomes we experience. Our health, financial well-being, and even likelihood of divorce are all influenced by the company we keep--and the company those people keep.

Choose Your Network

When you take a job, you're adopting a readymade social network, and they become a large and influential part of your life. Your co-workers are people you spend much, if not most, of your time with.

Asking yourself one simple question can illuminate the potential impact of the network. The question is: Do I want to be like these people?

It's best to ask this before joining an organization, taking a job, or even getting married. Once you're committed, it's much harder to see things clearly, since we tend to be biased in favor of groups we are already a part of.

Think about these people (and their networks). Do they have the things you want for yourself? Are they happy? Do they have good marriages, good health, and supportive communities? Are they people you want to be like?

Before taking (or staying in) that job, consider carefully not only the product, pay, and purpose of the organization, but also the social network you'll be joining. While you may exert influence on your new co-worker community, remember that they, and their friends and families, will also be exerting influence on you.

As leaders of organizations who want to attract top performers, look around your own culture and ask yourself if the people in it are healthy, happy, and productive. Put yourself in prospective employees' shoes and ask yourself if you measure up.

Resources: For more about the influence of networks read "Connected: The Surprising Power of Our Social Networks and How They Shape Our Lives" and watch Nicholas Christakis's TED Talk "The Hidden Influence of Social Networks."