The statement that "the higher the crystallinity, the more difficult it is to propagate" is not generally true, and it seems to be a misunderstanding of the relationship between crystallinity and mechanical properties. In materials science and engineering, the level of crystallinity in a material is typically not directly related to its ease of propagation or fracture. Instead, other factors like mechanical strength, toughness, and brittleness play a more significant role in determining how easily a material can propagate or undergo crack growth.