"Life is in Du Jie, and people who cross others will always cross themselves" means that life is like a robbery, and everyone needs to experience what he wants to experience to improve himself. In this process, helping others means helping yourself, because only by freeing yourself from difficulties can we help others better.
"Crossing people" refers to helping others to get from this side of reality to the other side of ideal, and "self-crossing" refers to getting rid of difficulties and reaching sublimation by one's own efforts. This sentence emphasizes the importance of self-crossing. Only by sublimating yourself first can we cross people better.