They have no root at the beginning so they can't suck up water and nutrition to grow but they are so strong that they can survive that harsh environment.
Here is one of my sweet potato's sprouts. It obviously looks dead. All leaves had gone. I guess novice gardeners might take they are truly dead and throw them away.
But don't give them up! They are still alive! They have no leave because of no water and nutrition to be sucked up but they were extending their roots in soil. In a photo below, taken a week ago, you can see the sprout have successfully been revived.
Now I've found all of my sprouts are healthy.