I read an interesting article from INC. today called "Are Your Employees Destroying your Business?".  It discusses the ways that the people we're around the most -- those we spend the most time with -- have a direct impact on our own psychology.  So, if your staff or coworkers are unpleasant and difficult to get along with, guess what?  YOU will begin to be the same way!  Even if you started out as an upbeat, positive person -- being surrounded by Eeyores will bring you down.  

Great point for businesses, and especially for smaller teams.  Nowadays, unless you're working for a major corporation, you're probably at a company where the teams consist of small groups.  Even at bigger companies, the typical day-to-day working group won't be huge... if "five people" are the magic attitude trigger, we need to pay close attention to the five people we spend the most time with.  And reality is that for most executives, we tend to spend more time with our work colleagues than we do with our own family; so the people we hire and work with are essential to our own mental health. Interesting to ponder, isn't it?