I usually say to myself that I am a good lock picker right before I find some 4 pin, no name lock with no security pins that kicks my butt.
If you pick one brand of lock hundreds of times you can't say, I can now pick "this brand" of lock with no problems.
Even if you say, I have picked this certain model of lock a million times, you still cannot say that you've mastered that model.
Or you can have a lock that you're very familiar with that someone pins up with different springs, weird pins, crazy MACS, etc..
Each individual lock, is an individual lock, and they bring their own quirks and problems.
You can talk to experienced pickers that have stories about the cheap little Master or Chinese lock that just stumped them.
I think Socrates and Gordon have it right.