At age 42, Lester Levenson, a physicist and successful entrepreneur, was at the pinnacle of worldly success, yet he was an unhappy, very unhealthy man. After he had his second heart attack, his doctors sent him home to die.

Lester realised his emotions were making him sick. He began a self-investigation by asking himself what he wanted out of life. His answer was happiness. He realised that negative emotions made him unhappy and that he felt happiest when he was loving rather than being loved. He developed the 'Sedona Method', a technique for letting go of negative emotions which is still being taught today. See this example of how the technique works.
Within three months, he had become healthy again, and claimed that he entered a state of profound peace which he sustained until he died, another 43 years later. Read his book No Attachments, No Aversions.