Motivational speaker Jim Rohn famously said that we are the average of the five people we spend the most time with.

This relates to the law of averages, which is the theory that the result of any given situation will be the average of all outcomes.

Salespeople, entrepreneurs and all successful people know that, in order to increase your wins, you've also got to increase your losses.

When it comes to relationships, we are greatly influenced — whether we like it or not — by those closest to us. It affects our way of thinking, our self-esteem, and our decisions. Of course, everyone is their own person, but research has shown that we're more affected by our environment than we think.

While it's ideal to be closely surrounded by positive, supportive people who want you to succeed, it's also necessary to have your critics. According to a study in the Journal of Consumer Research, "Tell Me What I Did Wrong: Experts Seek And Respond To Negative Feedback," novices have a preference for positive feedback, but experts want negative feedback, so that they can make progress.

And the more successful you become, the more criticism you'll face. Glenn Llopis over at Forbes wrote about how "6 Types Of People Build Your Mental Toughness," including doubters, critics, and the envious. Without them, you'd never sharpen your skills or develop tough skin.

It takes a while to develop this mental toughness. Just look at JCPenney CEO Ron Johnson. Critics are firing at him every day, but it's taken him several decades to get to this point where he can brush off harsh words from investors and the media.

Of course, Johnson must have a very tight inner network of confidants who support him no matter what. And that's the key to making it to the top in any industry.