🚀 go-pugleaf

There is something about relative humidity that I've been curious about for 
a while.  I am hoping that someone on the net could help me understand this.

From what I remember from my high school chemistry class, the relative humidity
(for a given location and time) is the ratio: 

	actual pressure of water vapor dissolved in the atmosphere 
	----------------------------------------------------------
	vapor pressure of water at the same temperature

where the vapor pressure is the equilibrium pressure of the vapor with its liquid
at a given temperature.

My question is, why is the relative humidity not always 100%?

Shouldn't the liquid water on the surface of the earth (which there seems to be
a plenty of) evaporate into the atmosphere and eventually reach an equilibrium,
thereby making the actual pressure of water vapor equal to the vapor pressure of
water?  (Think about a sealed jar partially filled with water.)  Can the concept 
of 'vapor pressure' be used in such a 'global' sense?  What other factors are 
there that influence the humidity?

Thanks in advance for any explanation.

Young Huh