Glory
It's a glorious day when you finally know every inch of the city, but it takes years to know a city that well. The day when you can argue cab routes with a native and actually win will be a memorable one.
Glory comes in other forms too, such as making enough during your shift to bring home a large profit, or meeting an interesting passenger (although we're sure you'll take the large profit over the interesting passenger any day). Taking good enough care of your interesting passenger and receiving a tip that makes you feel warm inside is a sweet combination of the two.
Most of the glory comes at the end of your shift. You've worked hard, maybe made a few new friends, and you're able to say you can make it to the airport five minutes faster than any other driver you know—even if you did leave a trail of destruction in your wake.