One way that often works for me: 1. Work very hard on the problem all day, no solution at sight. Looks like no solution exists. 2. Go home, eat, relax and go

One way that often works for me: 1. Work very hard on the problem all day, no solution at sight. Looks like no solution exists. 2. Go home, eat, relax and go bed. 3. The successive morning go to work. You will able to solve the problem in half an hour.