This is one of the negative superstitions which are still prevalent to this day. As the stories go, the origin of this was in a very dark time in our history. It was at a time when racism was at its peak throughout the world. Black men and women were tortured and killed on a daily basis without any law prohibiting it. This is why most people who know the origin of this superstition try to avoid speaking about it.
This superstition did not start like this, it used to be something like “step on a crack and your mother will turn black”. The meaning behind this shameless superstition is how hateful the racial bias was during that period. It implied that if you stepped on a crack on the road then you would be very unlucky, and to portray a measure of unluckiness it was said that a black person would enter your family.
This superstition can also be traced back to one more origin. This one is not really that much hate-filled, but it is much scarier to the believers. It is said that cracks in the pavement are links to the underworld and by stepping on one such crack you are inviting a demon to ruin your life, and this demon will haunt you and your family.
While one origin of this superstition is based on the presence of mythological demons living underneath the ground, the other one is a testament to the fact that our demons come from within. Whatever be the origin you follow, this is one dark superstition and even discussing it is equivalent to inviting suffering upon ourselves. It is much simpler to just avoid stepping on cracks so that we can avoid listening to anyone rhyming this line to us.