Why does the Jehovah's Witnesses say that, Jesus' second coming occurred in 1914?

My great grandmother was a JW. She believed that a man in Utah saw Jesus and he was given the things that a JW now believes. My grandmother was a very strange person. She gave all her money, which is not much to these people. There were points in her life that she could not feed herself but she was able to give them money. They believe that Jesus is coming back and taking only a small number of people to Heaven. I forget the number.