At the height of the Great Depression, Harvard scientists started tracking students in hopes of discovering the key to a long and happy life. They looked at participants' mental and physical health over 75 years. It is the longest study of happiness to date. 75 years and all they did was confirm what we've known since the beginning of time. The most powerful predictor of health and happiness is the quality if our relationships. Strong relationships protect us. Loneliness, on the other hand, can be deadly. Over the course of our lives, our relationships ebb and flow. We get together, break up, move away, or fall out of touch. It's prolonged periods of loneliness and toxicity that wreak havoc on our health, our brain function, and our longevity. Sometimes, being alone can be so terrifying that we trap ourselves in harmful relationships. But in order to really thrive, you've got to be ready to cut and run. Your life just might depend on it.