Happiness comes in so many different forms that it can be hard to define. Unhappiness, on the other hand, is easy to identify; you know it when you see it, and you definitely know when it’s taken ahold of you.
Unhappiness is lethal to everyone around you, just like second-hand smoke. The famous Terman Study from Stanford followed subjects for eight decades and found that being around unhappy people is linked to poorer health and a shorter life span.
Source: Troubling Habits of Chronically Unhappy People
My Comments: Good advice writing