As the Huffington Post points out, coloring books for adults are best sellers in France and the U.K. Hachette, a French publisher, has even capitalized on the trend by selling a 20_volume collection of stress_reducing coloring books called Art_Thérapie. Using coloring books to de_stress has been especially popular amongst French women, who have even taken to posting their creations on social media and forming Facebook groups to share coloring tips.
I think the biggest problem people have when drawing with crayons is that they regress to being five years old again. They hold the crayon like they're coloring again, instead of applying it like a fine art medium. Another problem is that many people want to make it perform like colored pencils. While similar in application, they are quite different. You should not use crayons and expect them to behave like colored pencils. You'll be setting yourself up for disappointment.