Consider a system with transfer-function $G\left ( s \right )=\dfrac{2}{s+1}$. A unit step function $\mu \left ( t \right )$ is applied to the system, which results in an output $y\left ( t \right )$. If $e\left ( t \right )=y\left ( t \right )-\mu \left ( t \right ),$ then $ \lim\limits_{t\rightarrow \infty }e\left ( t \right )$ is ___________________.