Yes they are … moods are contagious. And this is true for events: meeting someone or a group of people in a different state can change your day.
But what’s even more powerful, is what people can do to you continuously: your family, your colleagues, your friends … they have an everyday impact on your state. And state means approach to life. And approach to life means achieving goals. And achieving goals means happiness!
So when you have a chance to choose (for ex. a new job, a new candidate), keep into account also the ‘state’ this person will be able to bring to your life