This is one of those situations where the annalogy between electrical current and water flow can prove usefull. Suppose you poor water into one end of a hose. If you poor in 5 gal./min. at one end, then 5 gallons per minute will have to come out the other end. If you put a restriction somewhere in the hose, you'll need to apply more pressure at the one end in order to get those same 5 gallons per minute to flow in. If you place several more restrictions, you'll increase the amount of pressure needed. If the additional pressure is not applied, the rate of flow will slow down, but the amount of water flowing in one end will always be the same as the amount flowing out the other end, because there is "only one path"; nowhere else for the flow to go.