Thank you very much, sir.I understood very clearly.

Problem with P controllers is exactly that it results in steady state errors. Hence, PI controllers! Here (attached) is a link that explains better.

https://softwareengineering.stackexchange.com/questions/214912/why-does-a-proportional-controller-have-a-steady-state-error

By increasing the value of proportional gain, Kp, or by resetting the operating point to obtain zero steady state error using P-controller.