Why do people with obsessive-compulsive-disorder avoid stepping on lines?
People with OCD tend to count things and sometimes challenge themselves by doing different things. This particular thing could be that the person wanted to see how many times he/she could avoid stepping on lines or maybe the lines mean something to him/her and they are avoiding it. This person could also be counting; maybe only allowing themselves four steps per square of cement without stepping on the lines. It’s just a guess, hope it made some sense to you. God bless you.