For the sigmoid function σ(X) = 1/(1+e^(-X)), choose the approximate value of X=k from where you start seeing that the sigmoid curve is asymptotic to the line σ=1

DL#103 Sigmoid Neuron Sigmoid Neuron Using Python
For the sigmoid function σ(X) = 1/(1+e^(-X)), choose the approximate value of X=k from where you start seeing that the sigmoid curve is asymptotic to the line σ=1.
It ans is k = 1 Why
Can anyone explain, please !!!