in a fountain pen, ink does not run out by its own. why?

Fountain pen has a reservoir in it to store ink into it. The nib of the pen take ink through the reservoir via gravity and capillary action. Capillary action under which with which the liquid to flow against the gravity and rise to the thin walls of the capillary. This involves the adhesion and cohesion forces. Due to this capillary action the flow of ink controls in the pen.