OK. There are buses that go to Dulles International Airport (which the transportation industry abbreviates to IAD; I suppose the transportation industry is French or something?) And there is at least one bus (or bus LT, anyway) that will take you from Dulles to various points between IAD and Dulles Town Center. The smaller local bus is the Loudoun County Transit Dulles 2 Dulles Connector. (Isn't it cute when they use a "2" in place of "to"? It's like they're trying to be all hip and text-messagey or something.) The D2D is scheduled to meet the passengers of MetroBus 5A, which runs every hour or so.
The important thing to know is that the MetroBus drops you off on the lower deck of IAD and the Loudoun County Transit bus picks you up at position 2E. Position 2E, oddly enough, is also on the lower deck.
This is important to know, because your Metro driver may not be aware of this. In fact, your Metro driver may suggest -- nay! outright tell you with certainty -- that the Loudoun County Transit bus takes passengers from the upper deck. And if you listen to this sad sack, you will walk into the terminal and climb to the upper deck. You will wander around looking for the Loudoun County Transit bus, but it will not be there. You will eventually meander over to the IAD information desk and the attendant will tell you that the D2D Connector picks up at position 2E, which is, as you now know better than the Metro driver did, is on the lower deck, mere paces from where the Metro bus 5A drops off.
However, if you had listened to the Metro driver, you would now be at position 2E ten or maybe even fifteen minutes too late to catch the D2D Connector. You might decide then to wait for the next bus, which, you'll know, arrives hourly.
On the other hand, you might decide that your customer meeting is too important to be half an hour late for, and you'll decide to take one of the conveniently available taxi cabs. Then, you'll find that IAD provides a monopoly to one brand of taxi cabs and a short trip up the road that would cost 50 cents on the shuttle lightens your wallet by $12.25.
It could happen.