I got my start as a courier after I was fired from a bank job. I didn't want my next job to be a "girlie" job, so it was either this or do landscape work. I needed a paycheck. I had no idea of what the money would be like. If I did, I probably wouldn't have done it.
When I first started riding, the thing I loved most was riding fast. Now, after 10 years, my focus is on doing the job as efficiently as I can without hurting myself. You start to focus more on timing. You have to know how to ride your bike when there is money on the line. You know how to say a certain thing to get something done, how to say hello to a receptionist to get your package faster. Each building has its own fingerprint and its own system for what you need to do to access it most efficiently.
Pedestrians and people on the street complain. They have an element of complete and total surprise -- they just didn't see the courier coming. Pedestrians are constantly coming into the street without looking. Cars often don't signal where they are going and don't look before they drive. The courier yells, like any rational person who thinks they are about to get hit by a car. You can't hear a bicycle bell through a Lexus. People are frustrated -- so they start yelling. Too much negative energy.
Each city shapes the attitude or persona of the couriers that work there. New York City is brutal to couriers, so couriers have to be more loud and obnoxious to survive. In D.C., the couriers are pretty polite and professional for the most part. Here you work in a world of embassies, government agencies, Congress and lobbyists. You have to know how to complete and file visa applications for people and you may have to stand in line for Senate hearings.
In the U.S., biking is looked at as a leisure activity or the kind of work that is on par with McDonald's. People should think of couriers as skilled professionals. This is an honest-to-God job.