Crossing the river with stones means that when people cross the river, sometimes the water flow of the river is very urgent, and it is easy to rush people away, if they are holding a very heavy stone, they will walk steadily to the other side of the river, if they do not hold stones, it is easy to be washed away
Therefore, wise people walk slowly in the river with a stone in their arms, which is buoyant by the water and not too heavy
Should be feeling the stones across the river! He means playing it safe, learning as you go