Sometimes, buying two plane tickets is cheaper than buying one. Although it's less convenient, building your own itinerary by buying a ticket to one city and then flying to your destination could save you a whole lot of dough.
The Wall Street Journal outlines this strategy as well as example savings. The reason fares are cheaper with this two-ticket strategy is often because deals are only available from certain cities (usually international gateway airports):
The tactic can work best in summer when discount airfares are harder to find. For a June 11 to 18, the lowest round-trip airfare from Atlanta to Berlin was priced on Friday at $US1,541. The New York to Berlin fare was $US680. With discount competition between New York and Atlanta, the lowest round-trip are to JFK was $US258. That is a savings of 39%, or $US2,400 for a family of four.
As mentioned, the huge savings do come with a cost: you will have to claim and recheck bags, go through security again, and make sure you have enough time to make your connection. It's something to consider when you're planning for your next trip.
A Trick for Cheaper Flights Hiding in Plain Sight [Wall Street Journal]