The human brain cannot do more than one thing at a time.

 

So when you press your head, the use of hands and the feeling of comfort go together but since the brain cannot fully perform two tasks at once, it manages the hand a little at a time and receives the feeling another time.So less comfort is available.

But when another person presses his head, the brain only takes the feeling.  There is only one thing to do together, there is no need to do another, so there is more comfort.