What is the main conflict in Time and Again by Jack Finney?

This novel of speculative fiction tells the story of a lonely, frustrated artist in New York City who journeys back and forth through time. It is in many ways written in the tradition of similar novels written by H.G. Wells and Jules Verne, using real-life science as a springboard for a narrative that explores the possibilities of what might happen if the principles behind that science were taken further. Within that context, the novel explores themes of personal responsibility and the relationship between past and present.