I believe excitement 'jumps'! If someone is excited, enthusiastic and passionate about something, they 'infect' those around them with the virus! Of course, some people are more susceptible to the enthusiasm virus.
Why choose to be someone, or hang around anyone, who dampens enthusiasm: a wet blanket who puts out the fire of life? Make a decision and choose to be enthusiastic about most things. Every task you do, do it with energy and vitality. Even if it is vacuuming the floor!