If you want to build a great business, you have to be very deliberate about whom you let into it.

Emotions and behaviors may circulate through social networks in patterns similar to what's seen in epidemiological models of the flu virus.

Every positive person you let into your life increases your chances of being positive 11 percent, estimated a study published in 2010 in the Proceedings of the Royal Society.

"Just one sad friend was needed to double an individual's chance of becoming unhappy," Wired summarized about the report.

Figuring out whom to avoid and whom to let in won't always be easy. But with a little practice, you can get really good at staying far away from people who might bring your business down.

Here are 10 people (whether employees or clients) you should avoid if you're starting a business:

1. The siren.

Sirens are those amazing and enticing people who come into your business and completely distract you. More than anyone else, these people have a way of stealing your focus and throwing your efforts off track.

A lot of promising futures have been sacrificed to sirens. Some people have sold their businesses for way less than they are worth and others have given up on their businesses to chase a get-rich-quick scheme than some sirens pitched them. Don't let this happen to you. Don't let an amazing person make you forget that you and your business have something amazing to offer the world, too.

2. The goat.

Goats are those wildly charismatic, big-talking and full-of-luck people who seem to get away with everything. These people have many strengths.

The problem is that they use their strengths in devious ways. Goats have little ambition beyond convincing others to make bad decisions. If you find yourself constantly making bad business decisions every time you're around someone in particular, it's time to cut that person out of your business.

3. The elephant.

An elephant never forgets. Elephants are those people in your business who never let you live down past mistakes. They never let you live down who you used to be or how many times you've messed up.

Don't let an elephant pull you back into the past. Everyone fails, especially entrepreneurs. If you've failed, it means you've learned. So stay on track and keep moving forward.

4. The hater.

Haters are people who want to be on top but don't want to work to get there. Instead, they want to push everyone else around them down so it will seem like they're on top.

Haters are losers but they also can serve as a source of motivation in a strange way. Don't let haters into your business but use them as motivation to make your business as strong as possible.

5. The narcissist.

Narcissists are talented people who are too consumed with themselves to take action. They're especially bad at taking team-oriented action.

A narcissist might even encourage you to put the image of your business over its reputation. This is always bad idea. When starting a business, it's best to be transparent and authentic. Don't try to make things seem bigger than they are and avoid trying to be something you're not. Instead, be real. Keep narcissists out of your startup and stay focused on your reputation, not your image.

6. The nemesis.

When you're starting a business, sometimes you'll have to work with someone whom you can't stand and who can't stand you. If you're not careful, this can become a major distraction.

Try to realize that what you don't like about a nemesis is probably something you don't like about yourself or it's something that you like too much about yourself. Either way, something is at odds with your identity and the only way to fix it is to turn the mirror on yourself, not the nemesis.

Your adversary can be your advisor in a way. If you bring a nemesis into your startup, use this person to learn about yourself. Once you do this, he or she won't be your nemesis anymore.

7. The Ares.

Ares is the Greek god of war. Ares-type people love conflict. They are addicted to drama and winning at all costs, even if there's nothing to be won. Any time spent trying to correct or even understand an Ares is a waste of time. You are better off ignoring these people and keeping them out of your business altogether.

8. The Dionysus.

Dionysus is the Greek god of wine, parties and pleasure. Dionysus sorts are pleasure seekers who have very little patience for anything other than instant gratification.

Be careful when letting these people into your business because base pleasure of any kind is both addictive and time-consuming. It's important to have friends and have fun, but you should never sacrifice your startup to a string of late nights.

9. The black cat.

Some people can walk into a business and light it up. Others walk in and kill it. Black cats are the latter. They are the people who seem to have a dark cloud following them everywhere they go.

These people are unlucky, negative and always depressed. Don't feel bad for these people. Odds are, they like sitting in the pits. They like the attention it gives them. So, let them sit. Just make sure they're sitting outside your business.

10. The fat cat.

Fat cats are those people who will come into your business, throw a bunch of money around and offer you the world. Whether these people are angel investors or venture capitalists from top firms, don't let their flash or their cash distract you from the fact that they want to control your company and make money off you.

Be very careful with whom give your business to. You didn't work this hard to watch your brand and reputation go down in flames at the paws of some fat cat who is now calling the shots.