So what's so great about position?

I've been playing NLHE for about a year, and have had decent success. I am basically a tight-aggressive player, bet the goods and mix in a few bluffs. One concept I have never been able to get a good handle on is position. I hear pros on TV make statements like "Position is ecerything." or "90% of my chips in this tourney came from playing position."

But I just don't get it. I see the basic advantage, like picking up an occasional orphan pot if checked around to the button. But how can some players say position is "everything?" I bought HOH and he doesn't even have "position" in his Index, though he refers to it quite often in the text.

Does anyone know of a good way to explain why position is so important and how to use it to your advantage? Hand histories where position is utilized would probably be very helpful as well.

Thanks

Highlander