Can negative thoughts make positive results?

Do negative thoughts always cause negative actions and unwanted results? Can‘t we say that sometimes a negative thought could make a positive result? How can we explain this?

For example, I have a friend who wanted to lose weight. He started to write down negative things like curses about himself on sticky notes and stick them on the fridge and doors and other places in his house. Then he started to lose weight. He said that the negative talk was his motivation and helped him stop overeating. And he was so happy with the result!

And also I heard Brooke said that her mother in law lived 5 years more because she was afraid to die and go to hell. So a negative thought and negative feeling, made a better result for her.