The function with variables x and y and a konstant k provided such that xy=k has strong stabilty in y when x is very large.
i.e. a bit of change in x (for large x values) is not going to disturb the value of y as much as x does.
D(xy)=0 => xDy+yDx=0
===> Dy=-k/sqr(x) * Dx
for larger values of x the change Dx is vanishes to Dy.
P.S: same can be applied for y variable though.