A Gurmukh is ready to listen to the Guru.
Gurmukh literally means one who has his face towards the Guru, and manmukh is one who has turned his back towards the Guru. It means that the gurmukh is ready to listen to the Guru and follow his advice, whereas the manmukh follows his own mind and is incapable of listening to the Guru.
The gurmukh recognises that he knows nothing and looks up to the Guru to enlighten him and lead him. The manmukh thinks he knows everything because he has a fertile mind that is forever talking to him.
The gurmukh realises that his mind is just like a window, a keyhole through which he cannot see the whole sky. The manmukh looks through the keyhole (mind) and thinks he has seen the whole sky.
The manmukh acts according to the tiny picture he can see whereas the gurmukh places the Guru’s word above his own limited understanding and allows the Guru to lead him.
The Guru is the link between the gurmukh and the divine. The Guru has seen the bigger picture and can guide the disciple if the latter would let him. The gurmukh allows it and benefits by it; the manmukh does not allow it and goes astray.