The maps that you have for your GPS may not be current. This isn't something you necessarily think about before venturing out, but it is something to consider.
I had to pick my hubby up from the airport yesterday in DC. I got most of the way there without much incident, but when the GPS told me to take exit (number) B/A, I was at a loss. I was relying on him to get my directionally challenged self to the airport on time. What I didn't know was that these exits had been split off from each other at some point, so they were totally separate exits. This left me with little time to decide whether he meant A or B and by then, I'd blown by.
"Recalculating!" He seemed to scream at me. I began to wonder if the next generation of GPS would include phrases such as, "You're an idiot, I said turn left!" or some other such thing. I would like to recommend developers create a setting for the intensely nervous and directionally challenged folks that include more coddling. In heavy traffic, getting right in a half a mile is sometimes difficult, especially with the ultra-aggressive DC crowd. Saying things like, "Yes, you're going the right way" or "You can relax now" would be ideal for me!
I made it to the airport with a bit of time to spare, though if my GPS were a real person, we might have come to blows. He told me to stay left and then suddenly I had to cross 3 lanes to exit. He did this to me several times. If everyone is relying on their GPS for good directions, it is no wonder people cut you off!